Ch. 17 - Chemical ThermodynamicsWorksheetSee all chapters
All Chapters
Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
BONUS: Mathematical Operations and Functions
Ch.4 - Chemical Quantities & Aqueous Reactions
Ch.5 - Gases
Ch.6 - Thermochemistry
Ch.7 - Quantum Mechanics
Ch.8 - Periodic Properties of the Elements
Ch.9 - Bonding & Molecular Structure
Ch.10 - Molecular Shapes & Valence Bond Theory
Ch.11 - Liquids, Solids & Intermolecular Forces
Ch.12 - Solutions
Ch.13 - Chemical Kinetics
Ch.14 - Chemical Equilibrium
Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
Ch.18 - Electrochemistry
Ch.19 - Nuclear Chemistry
Ch.20 - Organic Chemistry
Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds

Thermodynamics is the branch of physical science concerned with heat and its transformations to and from other forms of energy. 

Spontaneous & Nonspontaneous Reactions

Concept #1: Understanding Spontaneity

A reaction that requires no outside energy source is classified as a natural process and is spontaneous. 

A reaction that requires a continuous energy source to happen is classified as an unnatural process and is nonspontaneous. 

Practice: Which of the following statements is/are true?

a) The rusting of iron by oxygen is a non-spontaneous reaction.

b) The addition of a catalyst to a reaction increases spontaneity.

c) The movement of heat from a cold object to a hot object is a non-spontaneous reaction.

d) The diffusion of perfume molecules from one side of a room to the other is a non-spontaneous reaction.

e) None of the above. 

Additional Problems
What is true for the following reaction under standard condition? C2H6 (g) → C2H4 (g) + H2 (g) ΔH° is 137 kJ and ΔS° is 120 J/K a) spontaneous at all temperatures b) spontaneous only at high temperature c) spontaneous only at low temperature d) not spontaneous at all temperatures e) cannot be determined
The sublimation of solid carbon dioxide is a spontaneous process. Predict the sign (+, -, or 0) of ∆Gº r , ∆Hº r , and ∆Sº r , respectively. 1. -, -, - 2. 0, +, + 3. -, 0, + 4. -, +, - 5. -, +, + 
Consider the equation carefully, and think about the sign of ∆S for the reaction it describes. NH4Br (s) → NH3 (g) + HBr (g) ∆H = +188.3 kJ. Which response describes the thermodynamic spontaneity of the reaction? 1. The reaction is spontaneous only at relatively high temperatures. 2. All responses are correct 3. The reaction is spontaneous at all temperatures. 4. The reaction is not spontaneous at any temperatures. 5. The reaction is spontaneous only at relatively low temperatures.
Which statement best describes spontaneous reactions? a) Spontaneous reactions occur very quickly b) Spontaneous reactions can proceed without any external input c) The reverse of a spontaneous reaction is also spontaneous reaction d) All spontaneous reactions are reversible reactions e) Most spontaneous reactions become less spontaneous at high temperatures
A mixture of hydrogen and chlorine remains unreacted until it is exposed to ultraviolet light from a burning magnesium strip. Then the following reaction occurs very rapidly: H2 + Cl2      →       2 HCl       ΔG = - 45.54 kJ                                               ΔH = - 44.12 kJ                                               ΔS = - 4.76 J/k Select the statement below which BEST explains this behavior. A. The reactants are thermodynamically more stable than the products. B. The reaction has a small equilibrium constant. C. The ultraviolet light raises the temperature of the system and makes the reaction more favorable. D. The negative value for ΔS slows down the reaction. E. The reaction is spontaneous by thermodynamics, but the reactants are kinetically stable.
Given the following reaction: A(g) ⇌ B(g), the forward reaction is spontaneous under standard conditions. Which of the following statements must be TRUE? I.                The reverse reaction is nonspontaneous under standard conditions. II.              A(g) will be completely converted to B(g) if sufficient time is allowed. III.             A(g) will be completely converted to B(g) rapidly.   A) none of these B) I and I C) I, II, and III D) I E) II and III
For the reaction A + B ⇌ C + D, ΔH°= +40 kJ and ΔS°= +50 J/K. Therefore, the reaction at standard conditions is A. spontaneous at temperatures less than 10 K. B. spontaneous at temperatures greater than 800 K. C. spontaneous only at temperatures between 10 K and 800 K. D. spontaneous at all temperatures. E. Nonspontaneous at all temperatures.
Reactions with positive values of ∆S º r always become spontaneous at low temperatures. 1. False 2. True
A spontaneous chemical reaction is FAVORED by which of the following? A. increasing energy and increasing entropy B. lowering energy and increasing entropy C. increasing energy and decreasing entropy D. lowering energy and decreasing entropy
A reaction has a standard entropy change of +32.83 J/K and a standard enthalpy of +8.10 kJ. At what temperature is the reaction spontaneous? Assume the enthalpy and entropy of reaction are independent of temperature. a) Spontaneous when T > 246.7 K b) Spontaneous when T < 246.7 K c) Spontaneous when T > 25 K d) The reaction is non-spontaneous at all temperatures e) The reaction spontaneous at all times
Which reaction below is most likely spontaneous at any temperature? a. CH3CH2OH (g) → CH3CH2OH (I) b. 2 H2 (g) + O2 (g) → 2 H2O (g) c. C6H6O6 (s) + 6 O2 (g) → 6 CO2 (g) + 6 H2O (I) d. CO2 (s) → CO2 (g) e. None of the above
What factor ultimately determines whether any physical process, including a chemical reaction, is spontaneous or not? a) the change in entropy of the components involved in the process b) the change in enthalpy of the components involved in the process c) the change in enthalpy of the universe d) the change in entropy of the universe e) the change in entropy of the world outside the process f) the change in enthalpy of the world outside the process
Consider the following facts: water freezes spontaneously at -5 °C and 1 atm, and ice has a more ordered structure than liquid water. Explain how a spontaneous process can lead to a decrease in entropy.
For the process O2 (g) → 2 O (g), ΔH ° = + 498 kJ. What would be predicted for the sign of ΔSrxn   and the conditions under which this reaction would be spontaneous? ΔSrxn                             Spontaneous             a)     positive            at low temperatures only             b)     positive            at high temperatures only             c)     negative           at high temperatures only             d)     negative           at low temperatures only
At 25 oC, ΔHo = 1.895 kJ and ΔSo = – 3.363 J/K for the transition  C (graphite) →  C (diamond) Based on their data a) Graphite is more stable than diamond below 290 oC and diamond is more stable than graphite above 290 oC.  b) Graphite cannot be converted to diamond at 1 atm pressure.  c) Diamond is more stable than graphite at all temperatures at 1 atm.  d) Diamond is more stable than graphite below 290 oC and graphite is more stable than diamond above 290 oC. 
For each of the following chemical processes, state whether ΔS and ΔG are positive, negative,essentially zero, or undeterminable (based on the information provided).  
Which of the following processes WILL NOT be spontaneous at 1000 K? A)        ΔH = +40.2kJ/mole      ΔS =  -41.8 J/mole K B)        ΔH = +40.2kJ/mole      ΔS =  +41.8 J/mole K C)        ΔH = -41.8 kJ/mole      ΔS =  +40.2 J/mole K D)        ΔH = +41.8 kJ/mole      ΔS =  -40.2 J/mole K E)         both A and D
When a liquid evaporates, which is true about the signs of the enthalpy and entropy changes? a) ΔH is positive, ΔS is postive b) ΔH is positive, ΔS is negative c) ΔH is negative, ΔS is positive d) ΔH is negative, ΔS is negative  
Consider the following facts: water freezes spontaneously at -5 °C and 1 atm, and ice has a more ordered structure than liquid water. Explain how a spontaneous process can lead to a decrease in entropy.
Which of the following is an example of a nonspontaneous process? A) ice melting at room temperature B) sodium metal reacting violently with water C) rusting of iron at room temperature D) a ball rolling downhill E) water freezing at room temperature
A spontaneous endothermic reaction always A) causes the surrroundings to get colder. B) bursts into flame. C) requires a spark to initiate it. D) releases heat to the surrroundings. E) results in an increase in ΔSsurr
Given that the normal freezing point of ammonia is -78°C. Predict the signs of ΔH, ΔS and ΔG for ammonia when it freezes at -80°C and 1 atm. NH3(l) → NH3(s)           ΔH        ΔS       ΔG A.         +         -         + B.         -         -         - C.         -         -         0 D.         -         +         - E.        +         +         0    
The combustion reactions of hydrocarbons are reactions where ΔH°< 0 and ΔS° > 0. Based on this information, which one of the following statements is true regarding these reactions? (a) At all T, K is < 1. (b) At all T, K is > 1. (c) At low T, K is < 1, but at high T, K is > 1. (d) At low T, K is > 1, but at high T, K is < 1. (e) Can’t determine from the information given.
The thermodynamic condition for a spontaneous process at constant T and P is A) ΔS > 0. B) ΔS < 0. C) ΔG < 0. D) ΔG > 0. E) ΔG° = 0.
Sodium carbonate can be made by heating sodium bicarbonate: 2 NaHCO3(s) → Na2CO3(s) + CO2(g) + H2O(g). Given that ΔH° = 128.9 kJ/mol and ΔG° = 33.1 kJ/mol at 25°C, above what minimum temperature will the reaction become spontaneous under standard-state conditions? A) 0.4 K B) 3.9 K C) 321 K D) 401 K E) 525 K
If a process has a ΔH = +48 kJ/mol and a ΔS = -130 J/mol K at what T will it become spontaneous? A) 298 K B) 273 K C) 369 K D) 642 K E) Never  
Which of the following statements is TRUE? (a) An exothermic process will always be spontaneous. (b) A process in which the entropy of the system increases will always be spontaneous. (c) An endothermic process can never be spontaneous. (d) A process in which the entropy of the surroundings increases will always be spontaneous. (e) An exothermic process that is accompanied by an increase in the entropy of the system will always be spontaneous.
When barium hydroxide is dissolved in water, the temperature of the solution increases. Which of the following statements regarding this dissolution process is TRUE? (a) The reaction is spontaneous at all temperatures. (b) The reaction is driven only by entropy. (c) The reaction is driven only by enthalpy. (d) The reaction is spontaneous only at low temperatures. (e) The reaction is spontaneous only at high temperatures.
For the reaction A2(g) + B(s) → A2B(g) ΔH° > 0 and ΔS° > 0 Which of the following statements is true? A. The reaction is spontaneous at low temperatures. B. The reaction is spontaneous at all temperatures. C. ΔH° becomes more positive as temperature increases. D. The reaction is spontaneous at high temperatures. E. The reaction is non-spontaneous at all temperatures.
You observe that carbon dioxide sublimes. Which of the following statements about the signs of this process is/are true? I) Work (w) is positive. II) Heat (q) is negative. III) Change in Gibbs free energy (∆G) is positive. IV) Change in entropy (∆S) is positive. 1. I and II 2. II and III 3. I, II and III 4. I only 5. IV only  6. III and IV
For the reaction given below, ΔH° = -1516kJ and ΔS° = -432.8J/K at 25°C SiH4(g) + 2O2(g) →  SiO2(g) + 2H2O(l)  The reaction is spontaneous: a. only below a certain temperature b. only above a certain temperature c. at all temperatures d. at no temperatures e. cannot tell from the information available.    
Kw for the auto-ionization of water, H2O(l) → H+(aq) + OH− (aq), is 1.0 × 10−14. What are the signs (+/−) of ΔS° and ΔH° for the reaction at 25°C? a) ΔS° = (+) and ΔH° = (+) b) ΔS° = (+) and ΔH° = (−) c) ΔS° = (–) and ΔH° = (+) d) ΔS° = (–) and ΔH° = (–)
Based on your knowledge of carbon allotropes, You can say that ∆G◦f of graphite is ________ and ∆G◦rxn of diamond → graphite is _______. 1. zero, negative  2. positive, positive 3. large, zero 4. zero, large 5. large, small 6. small, negative
Consider the following sets. Which one indicates a  NON-spontaneous reaction. A. ΔH° = -35 kJ; ΔS° = 40 J/K; and the temperature is 80°C. B. ΔH° = -19 kJ; ΔS° = -60 J/K; and the temperature is 10°C. C. ΔH° = -15 kJ; ΔS° = -40 J/K; and the temperature is 150°C. D. ΔH° = 25kJ; ΔS° = 70 J/K; and the temperature is 125°C. E. ΔH° = 20 kJ; ΔS° = 75 J/K; and the temperature is 80°C.
For the reaction 2 SO3(g) → 2 SO2(g) + O2(g) ∆H◦r = +198 kJ · mol−1 and ∆S◦r = 190 J · K−1 · mol−1 at 298 K. The forward reaction will be spontaneous at 1. temperatures above 1042 K.  2. temperatures below 1042 K. 3. all temperatures. 4. no temperature. 5. temperatures above 1315 K.
Consider a reaction that has a positive ΔH and a positive ΔS. Which of the following statements is TRUE? A) This reaction will be non-spontaneous only at high temperatures. B) This reaction will be non-spontaneous at all temperatures. C) This reaction will be spontaneous at all temperatures. D) This reaction will be spontaneous only at high temperatures. E) It is not possible to determine without more information.  
Solid ammonium nitrate is very soluble in water. When it dissolves, the solution becomes very cold. Based on this information alone, what are the most likely signs of ΔH ̊, ΔS ̊ and ΔG ̊? a) +, +, ‐ b) +, +, + c) +, ‐, ‐ d) ‐, ‐, ‐ e) ‐, +, ‐
Consider a 1.00 L solution of 0.150 M HCN (Ka = 4.9 * 10−10); Assume carbon is the central atom.  Indicate whether each statement is true or false.     A. There are more HCN molecules in the solution than CN− ions  B. The acid reaction (corresponding to Ka) would have a ΔG° < 0  C. Adding 0.150 moles of a strong base to this solution would make a buffer  D. HCN is polar and has a linear shape  E. The best Lewis structure would have a single bond and triple bond on C F. HCN would exhibit hydrogen bonds with water 
The following reaction is endothermic: 2 H2O (l) → 2 H2(g) + O2(g) Which of the following answers correctly describes the spontaneity: A. This reaction is always spontaneous B. This reaction is only spontaneous at low temperatures C. This reaction is only spontaneous at high temperatures D. This reaction is never spontaneous  
Ethane is C2H6. Consider the reaction below:  C2H6(g) ⇋ 2 Cgraphite(s) + 3 H2(g)  ∆G◦rxn = 7.86 kJ · mol−1 The decomposition of ethane is (spontaneous/non-spontaneous) and therefore ethane is (stable/unstable). 1. spontaneous, unstable 2. spontaneous, stable 3. non-spontaneous, unstable 4. non-spontaneous, stable  
The plot of change in free energy versus temperature (T) shown below corresponds to a process that is enthalpically ________ (favored, disfavored) and entropically _______ (favored, disfavored). Explain.
Consider the reaction: 2O(g) → O2(g) a) Predict the signs of ΔH and ΔS. (There is no need to consult thermodynamic data tables).  b) Is the spontaneity of this reaction dependent on temperature? Explain.
Above what temperature does the following reaction become spontaneous? FeO (s) + CO (g) CO2 (g) + Fe (g)                             ∆H = – 11.0 kJ ∆S = – 17.4 J/K   A. 191K B. 632K C. 298K D. Not enough information to determine E. Always spontaneous
When solid NH4NO3 is dissolved in water at 25°C, the temperature of the solution decreases. What is true about the signs of ΔH and ΔS for this process?  (A) ΔH is negative, ΔS is positive (B) ΔH is negative, ΔS is negative (C) ΔH is positive, ΔS is positive (D) ΔH is positive, ΔS is negative
For the reaction 2 SO3(g) → 2 SO2(g) + O2(g) ∆H◦r = +198 kJ·mol−1 at 298 K. Which statement is true for this reaction? 1. The reaction will not be spontaneous at any temperature. 2. The reaction will not be spontaneous at high temperatures. 3. ∆G◦r will be negative at high temperatures.  4. ∆G◦r will be positive at high temperatures. 5. The reaction is driven by the enthalpy.
The equilibrium constant for the reaction NH4Cl(s) → NH3(g) + HCl(g) is 1.1 × 10−16 at 25°C. If the equilibrium constant is 6.5 × 10 −2 at 300°C, which statement is correct? a) This is an enthalpy-driven reaction. b) The reaction is spontaneous at high temperatures. c) The reaction is spontaneous at all temperatures. d) The reaction is exothermic. e) The reaction is not spontaneous at any temperature.
The normal freezing point of ammonia is -78°C. Predict the signs of ∆H, ∆S, and ∆G for ammonia when it freezes at -80°C and 1 atm: NH3(l) → NH 3(s) 
Which of the following is a description of a phase change for which ΔG is positive.  A. Liquid water forming steam at standard pressure and 94°C B. Liquid water forming ice at standard pressure and -7°C C. Steam forming liquid water standard pressure and 30°C D. Ice forming liquid water at standard pressure and 5°C  
What would be the signs of ∆H and ∆S for the reaction AB4(g) → AB3(g) + B(g) ? 1. Both zero. 2. ∆H = +, ∆S = − 3. Impossible to tell from the information given. 4. Both positive.  5. ∆H = −, ∆S = 0 6. ∆H = 0, ∆S = − 7. ∆H = −, ∆S = + 8. Both negative. 9. ∆H = +, ∆S = 0 10. ∆H = 0, ∆S = +
For a reaction in which ΔH = 125 kJ/mol and ΔS = 325 J/K•mol, determine the temperature in Celsius above which the reaction is spontaneous. A.  385 °C             B.  273 °C       C.  112 °C       D.  405 °C       E.  25 °C  
For the reaction 2 C(s) + 2 H2(g) → C2H4(g)  ∆H°r = +52.3 kJ · mol−1 and ∆S°r =−53.07 J · K−1· mol−1 at 298 K. This reaction will be spontaneous at 1. no temperature.  2. temperatures below 985 K. 3. temperatures above 985 K. 4. temperatures below 1015 K. 5. all temperatures.  
Which of the following statements are true? I. In a spontaneous process, the path between reactants and products is reversible. II. The reaction of nitrogen atoms to form N2 molecules at 25° C and 1 atm is spontaneous. III. The melting of a solid is spontaneous above its melting point but nonspontaneous below its melting point. IV. The condensation of a liquid will be reversible if it occurs at any temperature other than the boiling point at a specified temperature. V. When a piece of metal is heated to 150° C and added to water, the fact that the water gets hotter is an example of a spontaneous process.    a) I, II, III b) II, III, IV c) II, III, V d) III, IV, V e) I, III, V  
Which of the following are the thermodynamic signs for the mixing of a gas with water? A. ΔH +, ΔS+ B. ΔH +, ΔS- C. ΔH -, ΔS+ D. ΔH -, ΔS-
Consider the conversion of a substance from solid to liquid. Solid ⇌ Liquid  At one atmosphere pressure and at the melting point of the substance, ________ . 
The following reaction is exothermic.                              N2 (g) + 3 H2 (g) → 2 NH3 (g) This means the reaction will be spontaneous in the forward direction at low temperature. is not spontaneous in the forward direction at any temperature. will be spontaneous in the forward direction at high temperature. is spontaneous in the forward direction at all temperatures.
The following reaction is endothermic:             2 H2O (l) → 2 H2 (g) + O2 (g) Which of the following answers correctly describes the spontaneity:             A.  This reaction is always spontaneous             B.  This reaction is only spontaneous at low temperatures             C.  This reaction is only spontaneous at high temperatures             D.  This reaction is never spontaneous
If a reaction is exothermic but experiences a decrease in its entropy, under what conditions is the reaction most likely to be spontaneous?   A. Low Temperature B. High Temperature C. Low Pressure D. High Pressure
For a certain chemical reaction,ΔH = 128 kJ/mol and ΔS = 64 J/ (mol × K) . What is the minimum temperature at which this reaction will be spontaneous?   A. 2 K                    B. 2000 K                     C. 2000 °C                     D. 2 °C
The reaction between elemental nitrogen and elemental hydrogen, shown below, is most kinetically and thermodynamically favorable.         N2 (g) + 3 H2 (g)   →    2 NH3 (g)  Based on this information, which of the following energy diagrams best describes this reaction? 
When ammonium ion and nitrate ion combine they form ammonium nitrate, NH4NO3. During this combination reaction the container feels cold to the touch. What are the signs for ∆H, ∆S, ∆G (at high T), and ∆G (low T)?     
Which of the following is required for a spontaneous reaction:   A. The entropy of the universe increases. B. The enthalpy of the universe increases. C. The Free Energy of the universe increases. D. The temperature of the universe increases. 
Which of the following is true regarding a non-spontaneous process:             I.    The process will occur with an outside influence             II.   The process will occur given sufficient time             III.  The process will never occur A.  only I         B.  only II       C.  both I and II          D.  only III      E.  None of the statements
The standard free energy of formation of CS 2 (l) is 65.27 kJ⋅mol −1 at 298 K. This means that at 298 K a) CS2 (l) will not spontaneously form C (s) + 2 S (s). b) CS2 (l) is thermodynamically unstable. c) CS2 (l) is thermodynamically stable. d) No catalyst can be found to decompose CS 2 (l) into its elements. e) CS2 (l) has a negative entropy.
Which reaction below is most likely spontaneous at any temperature?  a) CH3CH2OH (g) → CH3CH2OH (l) b) 2 H2 (g) + O2 (g) → 2 H2O (g) c) C6H6O6 (s) + 6 O2 (g) → 6 CO2 (g) + 6 H2O (l) d) CO2 (s) → CO2 (g) e) None of the above
Hot and cold packs are commercially available for both medical treatment and food storage. Ammonium chloride, NH4Cl, is commonly used in cold packs and is activated when it is dissolved in solution. What are the signs for ∆H, ∆S, ∆G (at high T) and ∆G (low T)? 
Two different gases occupy two separate bulbs. Consider the process that occurs when the stopcock separating the gases is opened, assuming the gases behave ideally.Is the process that occurs when the stopcock is opened a reversible one?
Indicate whether each of the following statements is true or false.A spontaneous process can in principle be conducted reversibly.
Indicate whether each of the following statements is true or false.Spontaneous processes in general require that work be done to force them to proceed.
What is a spontaneous process? Provide an example.
Explain the difference between the spontaneity of a reaction (which depends on thermodynamics) and the speed at which the reaction occurs (which depends on kinetics). Can a catalyst make a nonspontaneous reaction spontaneous?
Why do exothermic processes tend to be spontaneous at low temperatures? Why does their tendency toward spontaneity decrease with increasing temperature?
A standard air conditioner involves a refrigerant that is typically now a fluorinated hydrocarbon, such as CH2F2. An air-conditioner refrigerant has the property that it readily vaporizes at atmospheric pressure and is easily compressed to its liquid phase under increased pressure. The operation of an air conditioner can be thought of as a closed system made up of the refrigerant going through the two stages shown here (the air circulation is not shown in this diagram). During expansion, the liquid refrigerant is released into an expansion chamber at low pressure, where it vaporizes. The vapor then undergoes compression at high pressure back to its liquid phase in a compression chamber. Imagine that a sample of liquid refrigerant undergoes expansion followed by compression, so that it is back to its original state. Would you expect that to be a reversible process?
Free energy and approaching equilibrium. In the reaction N2 (g) + 3H2 (g) 2NH3 (g), if the reaction mixture has too much N2 and H2 relative to NH3 (left), Q<K and NH3 forms spontaneously. If there is more NH3 in the mixture relative to the reactants N2 and H2 (right) , Q>K and the NH3 decomposes spontaneously into N2 and H2.Why are the spontaneous processes shown sometimes said to be "downhill" in free energy?
Consider what happens when a sample of the explosive TNT is detonated under atmospheric pressure.Is the detonation a reversible process?
What are the criteria for spontaneity in terms of free energy?
What are the criteria for spontaneity in terms of entropy?
Spontaneity can depend on temperature. At T > 0 oC, ice melts spontaneously to liquid water. At T < 0 oC, the reverse process, water freezing to ice, is spontaneous. At T = 0 oC the two states are in equilibrium.In which direction is this process exothermic?
Indicate whether each of the following statements is true or false.The feasibility of manufacturing NH3 from N2 and H2 depends entirely on the value of H for the process N2 (g) + 3H2 (g)  →  2NH3 (g).
Indicate whether each of the following statements is true or false.Spontaneous processes are those that are exothermic and that lead to a higher degree of order in the system.
Two different gases occupy two separate bulbs. Consider the process that occurs when the stopcock separating the gases is opened, assuming the gases behave ideally.Predict the sign of H for the process.
Consider a system consisting of an ice cube.Under what conditions can the ice cube melt reversibly?
For each of the following processes, indicate whether the signs of S and H are expected to be positive, negative, or about zero.A solid sublimes.
For each of the following processes, indicate whether the signs of S and H are expected to be positive, negative, or about zero.The temperature of a sample of Co(s) is lowered from 60 oC to 25 oC.
For each of the following processes, indicate whether the signs of S and H are expected to be positive, negative, or about zero.Ethyl alcohol evaporates from a beaker.
For each of the following processes, indicate whether the signs of S and H are expected to be positive, negative, or about zero. A diatomic molecule dissociates into atoms.
For each of the following processes, indicate whether the signs of S and H are expected to be positive, negative, or about zero.A piece of charcoal is combusted to form CO2(g) and H2O(g).
Indicate whether G increases, decreases, or stays the same for each of the following reactions as the partial pressure of O2 is increased.2(l)  →  2 + O2(g)
Indicate whether G increases, decreases, or stays the same for each of the following reactions as the partial pressure of O2 is increased.2 KClO3(s)  →  + 3(g)
Consider the accompanying diagram, which represents how exttip{Delta G}{Delta G} for a hypothetical reaction responds to temperature.At what temperature is the reaction spontaneous?
Consider the vaporization of liquid water to steam at a pressure of 1 atm.In what temperature range is it a spontaneous process?
Consider the vaporization of liquid water to steam at a pressure of 1 atm.In what temperature range is it a nonspontaneous process?
Consider the vaporization of liquid water to steam at a pressure of 1 atm.At what temperature are the two phases in equilibrium?
At what temperatures is the following reaction, the reduction of magnetite by graphite to elemental iron, spontaneous? Fe3O4(s)+2C(s,graphite) →  2CO2(g)+3Fe(s)
Methanol (CH3OH) can be made by the controlled oxidation of methane: CH4(g) + O2(g)  →  CH3OH(g)Under standard conditions, is the reaction spontaneous at this temperature?
Consider the following reaction between oxides of nitrogen: NO2 (g) + N2 O(g)  →  3NO(g)Is the reaction spontaneous under standard conditions at this temperature?
Indicate whether each of the following statements is true or false.The reaction of Na(s) with Cl2 (g) to form NaCl(s) is a spontaneous process.
A standard air conditioner involves a refrigerant that is typically now a fluorinated hydrocarbon, such as CH2F2. An air-conditioner refrigerant has the property that it readily vaporizes at atmospheric pressure and is easily compressed to its liquid phase under increased pressure. The operation of an air conditioner can be thought of as a closed system made up of the refrigerant going through the two stages shown here (the air circulation is not shown in this diagram). During expansion, the liquid refrigerant is released into an expansion chamber at low pressure, where it vaporizes. The vapor then undergoes compression at high pressure back to its liquid phase in a compression chamber. Suppose that a house and its exterior are both initially at 31oC. Some time after the air conditioner is turned on, the house is cooled to 24oC. Is this process spontaneous or nonspontaneous?
Which of the following processes are spontaneous?The combustion of natural gas.
Which of the following processes are spontaneous?The extraction of iron metal from iron ore.
Which of the following processes are spontaneous?A hot drink cooling to room temperature.
Which of the following processes are spontaneous?Drawing heat energy from the oceans surface to power a ship.
Which of the following processes are nonspontaneous?a bike going up a hill
Which of the following processes are nonspontaneous?a meteor falling to Earth
Which of the following processes are nonspontaneous?obtaining hydrogen gas from liquid water
Which of the following processes are nonspontaneous?a ball rolling down a hill
Potential energy and free energy. An analogy is shown between the gravitational potential-energy change of a boulder rolling down a hill and the free-energy change in a spontaneous reaction. Free energy always decreases in a spontaneous process when pressure and temperature are held constant.Are the processes that move a system toward equilibrium spontaneous or nonspontaneous?
Explain why water spontaneously freezes to form ice below 0 oC even though the entropy of the water decreases during the state transition. Why is the freezing of water not spontaneous above 0 oC ?
For a chemical reaction to be spontaneous for standard conditions which of the following must be true? a) ΔH°rxn > 0 b) ΔS°rxn > 0 c) ΔG°rxn > 0 d) Both b and c e) None of the above
For a particular reaction, ΔH°sys = 40 kJ and ΔS°sys = 50 J/K. Under what temperature parameters is the reaction spontaneous?a. When T < 10 K.b. When T > 800 K.c. At temperatures between 10 K and 800 K.d. The reaction is spontaneous at all temperatures.e. The reaction is not spontaneous at any temperature.
At constant pressure, the following reaction is exothermic. The reaction (as written) is2NO2(g) → N2O4(g)a. spontaneous at all temperatures.b. spontaneous at low temperatures but not a high temperature.c. spontaneous at high temperatures but not a low temperature.d. not spontaneous at any temperature.e. More information is required to answer the question.
Consider the following reaction at 120°C. Which statement must be true?H2O(l) → H2O(g)a. The reaction is not spontaneous.b. The reaction is spontaneous.c. ΔG = 0d. ΔG < 0e. Two of these statements are true.
Which of the following reactions are spontaneous (favorable)?a) Reaction Fb) Reaction Ec) Reaction Dd) Reaction Ce) Reaction Bf) Reaction A
Above what temperature does the following reaction become nonspontaneous?2 H2S(g) + 3 O2(g) → 2 SO2(g) + 2 H2O(g)H= -1036 kJ; S= -153.2 J/K 
For the chemical reaction, A → B, choose the combination that is correct.A) ΔG < 0; Q > KB) ΔG < 0; Q < KC) ΔG < 0; Q = KD) ΔG° < 0; Q = KE) ΔG° < 0; Q < K 
Under standard conditions (298 K and 1 atm), which statement is true?i) diamond converts to graphite spontaneouslyii) graphite converts to diamond spontaneouslyiii) none of the above
Which of the following reactions are spontaneous (favorable)? 
For the decomposition of calcium carbonate, consider the following thermodynamic data.ΔH∘rxn =178.5kJ/mol, ΔS∘rxn = 161.0J/(mol⋅K)Calculate the temperature in kelvins above which this reaction is spontaneous. Express your answer to four significant figures and include the appropriate units.
Sodium carbonate can be made by heating sodium bicarbonate:2 NaHCO3 (s) → Na2CO3(s) + CO2(g) + H2O(g)Given that standard enthalpy of reaction is 128.9 kJ and the standard Gibbs energy of reaction is 33.1 kJ at 25oC, above what temperature is the reaction become spontaneous? Assume that the enthalpy and entropy of reaction do not depend on temperature.a) 0.4 Kb) 3.9 Kc) 321 Kd) 401 Ke) 525 K
Above what temperature does the following reaction become nonspontaneous?FeO(s) + CO(g) → CO2 (g) + Fe(s)ΔH = -11.0 kJ; ΔS = -17.4 J/K  
Which of these processes is spontaneous?a) the combustion of natural gasb) a hot cup of tea cooling to room temperaturec) the extraction of iron metal from iron oreIdentify the system and the surroundings, and for each spontaneous process, the constraint that has been removed to allow the process to occur.
Which of the following statements best describes an endothermic reaction?a) The reaction must be spontaneous at all temperaturesb) The reaction may become spontaneous at high T if ∆S rxn > 0c) The reaction may become spontaneous at low T if ∆S rxn < 0d) The reaction may become spontaneous at high T if ∆S rxn < 0
Which of the following is true regarding a non-spontaneous process: I. The process will occur with an outside influence II. The process will occur given sufficient time III. The process will never occur A. only I B. only II C. both I and II D. only III E. None of the statements
A reaction that is spontaneous as written _________. a. is very rapid b. will proceed without outside intervention c. is also spontaneous in the reverse direction d. has an equilibrium position that lies far to the left e. is very slow  
Which of the following processes are spontaneous? Select all that apply. a. a satellite falling to Earthb. water decomposing to H2 and O2 at 298 K and 1 atmc. average car prices increasingd. a soft-boiled egg becoming raw
Consider the reaction: FeO(s) + Fe(s) + O2(g)→ Fe2O3(s) Given the following table of thermodynamic data, determine the temperature (in C°) which the reaction is nonspontaneous. a. This reaction is spontaneous at all temperatures. b. 6180.1 c. 756.3 d. 2438 e. 1235
Which statement best describes the following endothermic reaction? C2H6(g) → C2H4(g) + H2(g) This reaction is ________. a. spontaneous at all temperatures b. spontaneous only at a high temperature c. spontaneous only at a low temperature d. nonspontaneous at all temperatures e. more information is needed to accurately describe the spontaneity of the reaction  
Above what temperature does the following reaction become non-spontaneous?H2S + 3O2 → 2SO2 + 2H2OΔH= -1036 kJΔS= -153.2 J/K
If a solute dissolves in an endothermic process a) H bonds must exist between solvent and solute. b) strong ion-dipole forces must exist in the solution. c) the solute must be a gas. d) the entropy of the solution is immaterial. e) the entropy of the solution must be greater than that of its pure components.
Based on the following graph below, determine the signs for enthalpy and entropy, respectively.  
A spontaneous chemical reaction is FAVORED by which of the following? a) increasing energy and increasing entropy b) lowering energy and increasing entropy c) increasing energy and decreasing entropy d) lowering energy and decreasing entropy
Which statement is true regarding the sublimation of dry ice (solid CO 2)?a. ΔH is positive, ΔS is negative, and ΔG is positive at all temperatures.b. ΔH is positive, ΔS is positive, and ΔG is positive at low temperature and negative at high temperature.c. ΔH is negative,ΔS is positive, and ΔG is negative at all temperatures.d. ΔH is negative, ΔS is negative, and ΔG is negative at low temperature and positive at high temperature.
Below what temperature does the following reaction become spontaneous?FeO(s) + CO(g)  → CO2(g) + Fe(g)    ∆H = -11.0kJ      ∆S = –17.4J/K191K632K298KNot enough information to determineAlways spontaneous
Fill in the blanks.
As a fuel, H2(g) produces only nonpolluting H2O(g) when it burns. Moreover, it combines with O2(g) in a fuel cell (Chapter21) to provide electrical energy.(a) Calculate ΔH°, ΔS°, and ΔG° per mole of H2 at 298 K.(b) Is the spontaneity of this reaction dependent on T? Explain.
What is a spontaneous reaction?
What is a nonspontaneous reaction?
Is the statement true or false? If false, correct it.(a) All spontaneous reactions occur quickly.
Is the statement true or false? If false, correct it.(b) The reverse of a spontaneous reaction is nonspontaneous.
Is the statement true or false? If false, correct it.(c) All spontaneous processes release heat.
Is the statement true or false? If false, correct it.(d) The boiling of water at 100°C and 1 atm is spontaneous.
Methanol, a major industrial feedstock, is made by several catalyzed reaction, such as CO(g) + 2H2(g) ⟶ CH3OH(l).(a) Show that this reaction is thermodynamically feasible.
Hydrogen cyanide is produced industrially by the following exothermic reaction:Is the high temperature needed for thermodynamic or kinetic reasons?
Consider two reactions for the production of ethanol:C2H4 (g) + H2O (g) → CH3CH2OH (l)C2H6 (g) + H2O (g) → CH3CH2OH (l) + H2 (g)Which would be the more thermodynamically feasible at standard conditions? Why?
Do all exothermic phase changes have a negative value for the entropy change of the system?
The Ostwald process for the commercial production of nitric acid involves three steps:c. Is there a thermodynamic reason for the high temperature in the first step, assuming standard conditions?
Acetylene is produced commercially by the partial oxidation of methane. At 1500°C and pressures of 1–10 bar, the yield of acetylene is about 20%. The major side product is carbon monoxide, and some soot and carbon dioxide also form.(c) Why must this reaction mixture be immediately cooled?
Consider the sublimation of iodine at 25.0 ˚C: I2(s) → I2(g)Explain why iodine spontaneously sublimes in open air at 25.0 ˚C.
Ethene (C2H4) can be halogenated by the following reaction: C2H4(g) + X2(g) ⇌ C2H4X2(g), where X2 can be Cl2, Br2, or I2.What is the main factor driving the difference in the spontaneity of the three reactions?CompoundΔH˚f (J/mol K)ΔS˚f (J/mol K)C2H4Cl2(g)–129.7308.0C2H4Br2(g)38.3330.6C2H4I2(g)66.5347.8
H2 reacts with the halogens (X2) according to the following reaction: H2(g) + X2(g) ⇌ 2 HX(g), where X2 can be Cl2, Br2, or I2.Reactant/ProductΔH˚f (kJ/mol)ΔS˚f (J/mol K) H2(g)0130.7Cl2(g)0223.1HCl(g)–92.3186.9Br2(g)30.9245.5HBr(g)–36.3198.7I2(g)62.42260.69HI(g)26.5206.6What is the main factor driving the difference in the spontaneity of the three reactions?
A helium-filled balloon spontaneously deflates overnight as He atoms diffuse through the wall of the balloon. Describe the redistribution of matter and/or energy that accompanies this process.
Many plastic materials are organic polymers that contain carbon and hydrogen. The oxidation of these plastics in air to form carbon dioxide and water is a spontaneous process; however, plastic materials tend to persist in the environment. Explain.
The major industrial use of hydrogen is in the production of ammonia by the Haber process:3H2 (g) + N2 (g) → 2NH3 (g)a. Using data from Appendix 4, calculate ΔH°, ΔS°, and ΔG° for the Haber process reaction.b. Is the reaction spontaneous at standard conditions?
Why does water spilled on the floor evaporate even though ΔG˚ for the evaporation process is positive at room temperature?
Consider the reactionFe2O3 (s) + 3H2 (g) → 2Fe (s) + 3H2O (g)a. Use ΔG°f values in Appendix 4 to calculate ΔG° for this reaction.b. Is this reaction spontaneous under standard conditions at 298 K?
A reaction is spontaneous under a certain set of conditions. Select all equations that must be true for this reaction under these conditions: ΔGrxn < 0, ΔGrxn > 0, ΔGrxn = 0, ΔG˚rxn < 0, ΔG˚rxn > 0, ΔG˚rxn = 0, ΔHrxn < 0, ΔHrxn > 0, ΔHrxn = 0, ΔSrxn < 0, ΔSrxn > 0, ΔSrxn = 0, Q = K, Q < K, Q > K
Consider the reaction: 3 O2(g) + 6 H2(g) + 6 C(s, graphite)  →  C6H12O6(s, glucose)Is this reaction spontaneous under standard conditions? What is the determining factor: the change in energy or the change in entropy or both? Explain.
Select the statements below that are false and why.a) If a chemical reaction is spontaneous then the ΔS sys must always be positive.b) If a chemical reaction with a negative ΔS sys is spontaneous then ΔSsurr must be positive.c) If a chemical reaction is spontaneous then the ΔEuniv must be increasing.d) We don't need to worry about spontaneous reactions because they are rare.
Consider the oxidation of carbon monoxide:CO(g) + 1/2O2(g) ⟶ CO2(g)(a) Predict the signs of ΔS° and ΔH°. Explain.
Consider the combustion of butane gas:C4H10(g) + 13/2 O2(g) ⟶ 4CO2(g) + 5H2O(g)(a) Predict the signs of ΔS° and ΔH°. Explain.
Replace each question mark with the correct information:
Among the many complex ions of cobalt are the following:Co(NH3)63+(aq) + 3en(aq) ⥫⥬ Co(en)33+(aq) + 6NH3(aq)where “en” stands for ethylenediamine, H2NCH2CH2NH2. Six Co—N bonds are broken and six Co—N bonds are formed in this reaction, so ΔH°rxn ≈ 0; yet K > 1. What are the signs of ΔS° and ΔG°? What drives the reaction?
It is quite common for a solid to change from one structure to another at a temperature below its melting point. For example, sulfur undergoes a phase change from the rhombic crystal structure to the monoclinic crystal form at temperatures above 95°C.a. Predict the signs of ΔH and ΔS for the process Srhombic (s) → Smonoclinic (s).
Two crystalline forms of white phosphorus are known. Both forms contain P4 molecules, but the molecules are packed together in different ways. The α form is always obtained when the liquid freezes. However, below -76.9°C, the α form spontaneously converts to the β form:P4 (s, α) → P4 (s, β)a. Predict the signs of ΔH and ΔS for this process.
Consider the reaction 2O (g) → O2 (g)a. Predict the signs of ΔH and ΔS.
When heated, the DNA double helix separates into two random coil single strands. When cooled, the random coils reform the double helix: double helix ⇌ 2 random coils.(b) Energy must be added to break H bonds and overcome dispersion forces between the strands. What is the sign of ΔG for the forward process when TΔS is smaller than ΔH?
When ammonium chloride is added to water and stirred, it dissolves spontaneously and the resulting solution feels cold. Without doing any calculations, deduce the signs of ΔG, ΔH, and ΔS for this process, and justify your choices.
Fill in the blanks in the table below where both ΔH and ΔS refer to the system.
One reaction used to produce small quantity of pure H 2 isCH3OH(g) ⇌ CO(g) + 2H2(g)(a) Determine ΔH° and ΔS° for the reaction at 298 K.(b) Assuming that these values are relatively independent of temperature, calculate ΔG° at 28°C, 128°C, and 228°C.(c) What is the significance of the different values of ΔG°?(d) At what temperature (in K) does the reaction become spontaneous?
A reaction that occur in the internal combustion engine isN2(g) + O2(g) ⥫⥬ 2NO(g)(a) Determine ΔH° and ΔS° for the reaction at 298 K.(b) Assuming that these values are relatively independent of temperature, calculate ΔG° at 100.°C, 2560.°C, and 3540.°C.(c) What is the significance of the different values of ΔG°?(d) At what temperature (in K) does the reaction become spontaneous?
As a fuel, H2(g) produces only nonpolluting H2O(g) when it burns. Moreover, it combines with O2(g) in a fuel cell (Chapter21) to provide electrical energy.(a) Calculate ΔH°, ΔS°, and ΔG° per mole of H2 at 298 K.(b) Is the spontaneity of this reaction dependent on T? Explain.(c) At what temperature does the reaction become spontaneous?
A reaction has ΔH°298 = 100 kJ/mol and ΔS°298 = 250 J/mol·K. Is the reaction spontaneous at room temperature? If not, under what temperature conditions will it become spontaneous?
Consider the following reaction occurring at 298 K: N2O(g) + NO2(g) ⇌ 3 NO(g)What temperature is required to make the reaction spontaneous under standard conditions?
Consider the decomposition of red mercury(II) oxide under standard state condition.2HgO(s, red) ⟶ 2Hg(l) + O 2(g)(b) Above what temperature does the reaction become spontaneous?
Magnesia (MgO) is used for fire brick, crucibles, and furnace linings because of its high melting point. It is produced by decomposing magnesite (MgCO3) at around 1200°C.(c) Assuming that ΔH° and S° do not change with temperature, find the minimum temperature at which the reaction is spontaneous.
Styrene is produced by catalytic dehydrogenation of ethylbenzene at high temperature in the presence of superheated steam.(b) At what temperature is the reaction spontaneous?
At what temperatures will the following processes be spontaneous?a. ΔH = -18 kJ and ΔS = -60. J/K
Propylene (propene; CH3CH=CH2) is used to produce polypropylene and many other chemicals. Although most propylene is obtained from the cracking of petroleum, about 2% is produced by catalytic dehydrogenation of propane (CH3CH2CH3): Because this reaction is endothermic, heaters are placed between the reactor vessels to maintain the required temperature.(f) At what temperature is the dehydrogenation spontaneous, with all substances in the standard state?
At what temperatures will the following processes be spontaneous?b. ΔH = +18 kJ and ΔS = +60. J/K
At what temperatures will the following processes be spontaneous?c. ΔH = +18 kJ and ΔS = -60. J/K
At what temperatures will the following processes be spontaneous?d. ΔH = -18 kJ and ΔS = +60. J/K
When heated, the DNA double helix separates into two random coil single strands. When cooled, the random coils reform the double helix: double helix ⇌ 2 random coils.(c) Write an expression for T in terms of ΔH and ΔS when the reaction is at equilibrium. (This temperature is called the melting temperature of the nucleic acid.)
The major industrial use of hydrogen is in the production of ammonia by the Haber process:3H2 (g) + N2 (g) → 2NH3 (g)c. At what temperatures is the reaction spontaneous at standard conditions? Assume ΔH° and ΔS° do not depend on temperature.
Consider the reactionFe2O3 (s) + 3H2 (g) → 2Fe (s) + 3H2O (g)c. The value of ΔH° for this reaction is 100. kJ. At what temperatures is this reaction spontaneous at standard conditions? Assume that ΔH° and ΔS° do not depend on temperature.
Consider the reaction2POCl3 (g) → 2PCl3 (g) + O2 (g)b. Is this reaction spontaneous under standard conditions at 298 K?
Consider the reaction2POCl3 (g) → 2PCl3 (g) + O2 (g)c. The value of ΔS° for this reaction is 179 J/K•mol. At what temperatures is this reaction spontaneous at standard conditions? Assume that ΔH° and ΔS° do not depend ontemperature.
Acetylene is produced commercially by the partial oxidation of methane. At 1500°C and pressures of 1–10 bar, the yield of acetylene is about 20%. The major side product is carbon monoxide, and some soot and carbon dioxide also form.(a) At what temperature is the desired reaction spontaneous:  2CH4 + 1/2O2    ⟶  C2H2 + 2H2 + H2O
Acetylene is produced commercially by the partial oxidation of methane. At 1500°C and pressures of 1–10 bar, the yield of acetylene is about 20%. The major side product is carbon monoxide, and some soot and carbon dioxide also form.(b) Acetylene can also be made by the reaction of its elements, carbon (graphite) and hydrogen. At what temperature is this formation reaction spontaneous?
Our atmosphere is composed primarily of nitrogen and oxygen, which coexist at 25 ˚C without reacting to any significant extent. However, the two gases can react to form nitrogen monoxide according to the following reaction: N2(g) + O2(g) ⇌ 2 NO(g).Is the reaction spontaneous?
Nitrogen dioxide, a pollutant in the atmosphere, can combine with water to form nitric acid. One of the possible reactions is shown below.Comment on the spontaneity of the reaction: 3 NO2(g) + H2O(l) → 2 HNO3(aq) + NO(g).
Indicate whether the following process is spontaneous or nonspontaneous:Liquid water freezing at a temperature below its freezing point
Indicate whether the following process is spontaneous or nonspontaneous:Liquid water freezing at a temperature above its freezing point
Indicate whether the following process is spontaneous or nonspontaneous:The combustion of gasoline
Indicate whether the following process is spontaneous or nonspontaneous:A ball thrown into the air
Indicate whether the following process is spontaneous or nonspontaneous:A raindrop falling to the ground
Indicate whether the following process is spontaneous or nonspontaneous:Iron rusting in a moist atmosphere
Which of the following processes are spontaneous?a. Salt dissolves in H 2O.b. A clear solution becomes a uniform color after a few drops of dye are added.c. Iron rusts.d. You clean your bedroom.
Which of the following processes are spontaneous?a. A house is built.b. A satellite is launched into orbit.c. A satellite falls back to the earth.d. The kitchen gets cluttered.
Which of these processes are spontaneous? (a) Water evaporates from a puddle. (b) A lion chases an antelope. (c) An isotope undergoes radioactive disintegration.
Which of these processes are spontaneous? (a) Earth moves around the Sun. (b) A boulder rolls up a hill. (c) Sodium metal and chlorine gas form solid sodium chloride.
Which of these processes are spontaneous? (a) Methane burns in air. (b) A teaspoonful of sugar dissolves in a cup of hot coffee. (c) A soft-boiled egg becomes raw.
Which of these processes are spontaneous? (a) A satellite falls to Earth. (b) Water decomposes to H2 and O2 at 298 K and 1 atm. (c) Average car prices increase.
Which process is spontaneous at 298 K?a. H2O(l) → H2O(g, 1 atm)b. H2O(l) → H2O(g, 0.10 atm)c. H2O(l) → H2O(g, 0.010 atm)
The evaporation of one mole of water at 298 K has a standard free energy change of 8.58 kJ.H2O(l) ⇌ H2O(g)         ΔG°298 = 8.58 kJ(a) Is the evaporation of water under standard thermodynamic conditions spontaneous?
One of the important reaction in the biochemical pathway glycolysis is the reaction of glucose-6-phosphate (G6P) to form fructose-6-phosphate (F6P):G6P ⇌ F6P             ΔG°298 = 1.7 kJ(a) Is the reaction spontaneous or nonspontaneous under standard thermodynamic conditions?
Which of the following processes are nonspontaneous? Are the nonspontaneous processes impossible?a. a bike going up a hillb. a meteor falling to Earthc. obtaining hydrogen gas from liquid waterd. a ball rolling down a hill
Methanol burns in oxygen to form carbon dioxide and water. Is the combustion of methanol spontaneous?
Which of the reactions are spontaneous as written. Check all that apply.a. PbO2(s) + 4H+(aq) + Sn(s) → Pb2+(aq) + H2O(l) + Sn2+(aq)b. O2(g) + 2H2O(l) + Ag(s) → 4OH−(aq) + 4Ag+(aq)c. Br2(l) + 2I−(aq) → 2Br−(aq) + I2(s)
Our atmosphere is composed primarily of nitrogen and oxygen, which coexist at 25 ˚C without reacting to any significant extent. However, the two gases can react to form nitrogen monoxide according to the following reaction: N2(g) + O2(g) ⇌ 2 NO(g).Does the reaction become spontaneous with increasing temperature?
Ethene (C2H4) can be halogenated by the following reaction: C2H4(g) + X2(g) ⇌ C2H4X2(g), where X2 can be Cl2, Br2, or I2.Does higher temperature make the reactions more spontaneous or less spontaneous?CompoundΔH˚f (J/mol K)ΔS˚f (J/mol K)C2H4Cl2(g)–129.7308.0C2H4Br2(g)38.3330.6C2H4I2(g)66.5347.8
H2 reacts with the halogens (X2) according to the following reaction: H2(g) + X2(g) ⇌ 2 HX(g), where X2 can be Cl2, Br2, or I2.Reactant/ProductΔH˚f (kJ/mol)ΔS˚f (J/mol K) H2(g)0130.7Cl2(g)0223.1HCl(g)–92.3186.9Br2(g)30.9245.5HBr(g)–36.3198.7I2(g)62.42260.69HI(g)26.5206.6Does higher temperature make the reactions more spontaneous or less spontaneous?
High level of ozone (O3) cause rubber to deteriorate, green plant to turn brown, and many people to have difficulty breathing. (a) Is the formation of O3 from O2 favored at all T, no T, high T, or low T?
Consider the following reaction occurring at 298 K: N2O(g) + NO2(g) ⇌ 3 NO(g)Can the reaction be made more spontaneous by an increase or decrease in temperature?
Consider the following reaction occurring at 298 K: BaCO3(s) ⇌ BaO(s) + CO2(g)Can the reaction be made more spontaneous by an increase or decrease in temperature?
The Haber process is very important for agriculture because it converts N2(g) from the atmosphere into bound nitrogen which can be taken up and used by plants. The reaction is N2(g) + 3 H2(g) ⇌ 2 NH3(g). This reaction is exothermic, but is carried out at relatively high temperatures. Why?
Methanol, a major industrial feedstock, is made by several catalyzed reaction, such as CO(g) + 2H2(g) ⟶ CH3OH(l).(b) Is it favored at low or at high temperatures?
Given the values of ΔH and ΔS, which of the following changes will be spontaneous at constant T and P?a. ΔH = +25 kJ, ΔS = 15.0 J/K, T = 300. Kb. ΔH = +25 kJ, ΔS = 1100. J/K, T = 300. Kc. ΔH = -10. kJ, ΔS = 15.0 J/K, T = 298 Kd. ΔH = -10. kJ, ΔS = 240. J/K, T = 200. K
Under what conditions is N2 O3(g) ⟶ NO(g) + NO2(g) spontaneous?
Which of the following statements is true?a. A reaction in which the entropy of the system decreases can be spontaneous only if it is exothermic.b. A reaction in which the entropy of the system increases can be spontaneous only if it is endothermic.c. A reaction in which the entropy of the system increases can be spontaneous only if it is exothermic.
Consider the signs for ΔHrxn and ΔSrxn for several different reactions. In which case is the reaction spontaneous at all temperatures?a) ΔHrxn < 0; ΔSrxn < 0b) ΔHrxn > 0; ΔSrxn > 0c) ΔHrxn < 0; ΔSrxn > 0d) ΔHrxn > 0; ΔSrxn < 0
Predict the spontaneity of a reaction (and the temperature dependence of the spontaneity) for each possible combination of signs for ΔH and ΔS (for the system).ΔH negative, ΔS positive
Predict the spontaneity of a reaction (and the temperature dependence of the spontaneity) for each possible combination of signs for ΔH and ΔS (for the system).ΔH positive, ΔS negative
Predict the spontaneity of a reaction (and the temperature dependence of the spontaneity) for each possible combination of signs for ΔH and ΔS (for the system).ΔH negative, ΔS negative
Predict the spontaneity of a reaction (and the temperature dependence of the spontaneity) for each possible combination of signs for ΔH and ΔS (for the system).ΔH positive, ΔS positive
Consider the reaction 2O (g) → O2 (g)b. Would the reaction be more spontaneous at high or low temperatures? 
Without doing a numerical calculation, determine which of the following will reduce the free energy change for the reaction, that is, make it less positive or more negative, when the temperature is increased. Explain.(a) N2(g) + 3H2(g) ⟶ 2NH3(g)(b) HCl(g) + NH3(g) ⟶ NH4 Cl(s)(c) (NH4)2 Cr2 O7(s) ⟶ Cr2 O3(s) + 4H2 O(g) + N2(g)(d) 2Fe(s) + 3O2(g) ⟶ Fe2 O3(s)
Predict under what temperatures (all temperatures, low temperatures, or high temperatures), if any, the reaction will be spontaneous.a. C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g), ΔH˚rxn = –2044 kJb. N2(g) + O2(g) → 2 NO(g), ΔH˚rxn = +182.6 kJc. 2 N2(g) + O2(g) → 2 N2O(g), ΔH˚rxn  = +163.2 kJd. 4 NH3(g) + 5 O2(g) → 4 NO(g) + 6 H2O(g), ΔH˚rxn = –906 kJ
Predict the conditions (high temperature, low temperature, all temperatures, or no temperatures) under which each of the following reactions will be spontaneous.a. H2O(g) → H2O(l)b. CO2(s) → CO2(g)c. H2(g) → 2 H(g)d. 2 NO2(g) → 2 NO(g) + O2(g) (endothermic)
Consider the reaction: 3 O2(g) + 6 H2(g) + 6 C(s, graphite)  →  C6H12O6(s, glucose)Is this reaction spontaneous under standard conditions? How do you know?
ΔG° = ΔH° - T ΔS°For the reaction Cu2O(s) + C(s) → 2Cu(s) + CO(g)a. would you expect a positive or negative change in entropy? Explain your answer. b. If this reaction is exothermic, under what temperature conditions (low, high or any) will this reaction be spontaneous?
A particular chemical reaction has a negative ΔH and a negative ΔS. Which statement is correct?(A) The reaction is spontaneous at all temperatures.(B) The reaction is non spontaneous at all temperatures.(C) The reaction becomes spontaneous as temperature increases.(D) The reaction becomes spontaneous as temperature decreases.
A particular chemical reaction has a negative ΔH and a positive ΔS. Which statement is correct?a) The reaction is spontaneous at all temperatures.b) The reaction is nonspontaneous at all temperatures.c) The reaction becomes spontaneous as temperature increases.d) The reaction becomes spontaneous as temperature decreases.
 Consider a reaction that has a positive ΔH and positive ΔS. Which of the following statements is TRUE?a. the reaction will be spontaneous at high tempsb. reaction will be spontaneous at all temps.c. reaction will be nonspontaneous at all temps.d. reaction will be nonspontaneous at high temps.e. not possible to determine without more information 
What can be said about an Endothermic reaction with a negative entropy change?The reaction isa. spontaneous at all temperatures.b. spontaneous at high temperatures.c. spontaneous at low temperatures.d. spontaneous in the reverse direction at all temperatures.e. nonspontaneous in either direction at all temperatures.
Suppose you have a system made up of water only, with the container and everything beyond being the surroundings. Consider a process in which the water is first evaporated and then condensed back into its original container.Is this two-step process necessarily reversible?
Making Methanol The element hydrogen is not abundant in nature, but it is a useful reagent in, for example, the potential synthesis of the liquid fuel methanol from gaseous carbon monoxide: 2 H2(g) + CO(g) --> CH3OH (g) This reaction is spontaneous at temperatures lower than:
If ΔH = -80.0 kJ and ΔS = -0.400 kJ/K, the reaction is spontaneous below a certain temperature. Calculate that temperature. Express your answer numerically in kelvins.
As shown here, one type of computer keyboard cleaner contains liquefied 1,1-difluoroethane (C2H4F2), which is a gas at atmospheric pressure. When the nozzle is squeezed, the 1,1-difluoroethane vaporizes out of the nozzle at high pressure, blowing dust out of objects.Based on your experience, is the vaporization a spontaneous process at room temperature?
For each phase change, determine the sign of ΔH and ΔS.Sublimation ,Freezing, Condensation, Deposition, Boiling , Melting a)   +ΔH,+ΔSb) -ΔH, -ΔSc) +ΔH, -ΔSd) -ΔH, +ΔSPut the phase change to the correct sign of ΔH and ΔS
Which of the following processes are spontaneous?a. Earth moving around the Sunb. A boulder rolling up a hillc. Sodium metal and chlorine gas reacting to form solid sodium chloride.
Two different gases occupy two separate bulbs. Consider the process that occurs when the stopcock separating the gases is opened, assuming the gases behave ideally.How does the process affect the enthalpy of the surroundings? 
For a particular reaction, delta Hº is 55.4 kJ/mol and delta Sº is 94.1 J/(molK). Assuming these values change very little with temperature, over what temperature range is the reaction spontaneous in the forward direction? 
What can be said about an endothermic reaction with a negative entropy change?The reaction is
The following generic reaction will always be spontaneous if the change in enthalpy is________ and the change in entropy is _________. negative, negativepositive, negative negative, positive positive, positive
For the following reaction, ΔH rxn = −120 kJ / mol-rxn and ΔS rxn = −150 J / mol-rxn•K:2NO(g) + O2(g) → 2NO2(g)At what temperatures will this reaction be spontaneous?Note: Remember that we can assume that the ΔH and ΔS values are approximately independent of temperature.Choose 1 answer:a. The reaction is never spontaneous, no matter what the temperature.b. The reaction is spontaneous when T < 800 K.c. The reaction is spontaneous when T > 800 K.d. The reaction is spontaneous at all temperatures.
Classify the following phase changes by the signs of the system's ΔH and ΔS.solid to liquid                gas to solidliquid to gas                  solid to gasliquid to solid                gas to liquid
Which of these statements are true? 
What can be said about an exothermic reaction with a negative entropy change?The reaction isa) spontaneous at all temperatures.b) spontaneous at high temperatures.c) spontaneous at low temperatures.d) spontaneous in the reverse direction at all temperatures.e) non-spontaneous in either direction at all temperatures.