Ch.13 - Chemical KineticsWorksheetSee 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

Rate Law represents an equation for a chemical reaction that connects the reaction rate with the concentrations or pressures of the reactants and the rate constant. 

Rate Law

When it comes to the rate of a reaction the Rate Law focuses on the reactant concentrations, while ignoring the product concentrations. 

Concept #1: Understanding the Rate Law. 

By focusing on only the reactant concentrations we only care about the forward direction of our chemical reaction. 

Concept #2: The Rate Determining Step. 

If the reaction says it’s a SLOW step or a ONE-STEP MECHANISM then we can simply look at the coefficients of the reactants to determine the reaction orders. 

Example #1: For the following reaction, use the given rate law to determine the best answer for the reaction with respect to each reactant and the overall order.

H2O2 (aq) + 3 I (aq) + 2 H+ (aq)  --->  I3 + 2 H2O (l)  

 

Rate = k [H2O2]2 [I ]

 

a) H2O2 is 1st order, I is 1st order, 2nd order overall.

b) H2O2 is 2nd order, I is 1st order, 3nd order overall.

c) H2O2 is 0th order, I is 1st order, H+ is 1st order, 3rd order overall.

d) H2O2 is 2nd order, I is 1st order, H+ is 0th order, 3rd order overall.

Example #2: Answer each of the following question based on the following chemical reaction:

Calculate the reaction order for reactant A. 

Practice: Calculate the reaction orders for Reactants B and C.

Example #3: Calculate the rate constant and the new rate for the given reaction if the initial concentration of [A] = 0.300 M, [B] = 0.150 M and [C] = 0.150 M.

The Rate Constant k

The Rate Constant k can have a direct impact on the rate of the reaction. In order to determine its units just utilize the equation below, where n is the overall order of the reaction: 

Example #4: A certain chemical reaction has the given rate law:

Rate = k [A]3 [B]2 [C]-1

What are the units of the rate constant for the given reaction?

a) M-2 s-1      b) M2 s-1       c) M-4 s-1      d) M-3 s-1      e) M3 s-1

Example #5: The reaction of 3 A + B ---> 2 C + D, was found to be: Rate = k [A]2 [B]3. How much would the rate increase by if A were tripled while B were increased by half?

a) 0.50              b) 30.38            c) 0.75              d) 20.25            e) 1.125

Practice: If the rate law for the following reaction is found to be the following, what are the units for the rate constant, K?

Cl2 (g) + HCCl3 (g) → HCl (g) + CCl4 (g)

a)          b)           c)           d)           e) 

Reaction Mechanisms

Concept #3: A   Reaction Mechanism   involves a series of elementary reactions that give the overall equation. 

Additional Problems
Consider a reaction with the following rate law Rate = k [C]2[D]3[E]-1 By what factor would the rate of the reaction increase if the concentration of [C] tripled, the concentration of D is increased by half and concentration of [E] doubled? A. 15.2 B. 12.9 C. 9.0 D. 6.5 E. 30.4
 The rate law for a reaction is Rate = k[A][B]2 Which one of the following statements is false? a. The reaction is second order in respect to B.  b. If [B] is doubled, the reaction rate will increase by a factor of 4. c. If [A] is doubled, the reaction rate will increase by a factor of 2. d. The reaction is first order overall. 
Determine the rate law for the reaction 2ClO2 (aq) + 2 OH - (aq) → ClO2- + H2O (l) given the following data. a. Rate = k[ClO2][OH-] b. Rate = k[ClO2]2[OH-] c. Rate = k[ClO2]2[OH-]2 d. Rate = k[ClO2][OH-]2 e. Rate = k[OH-]
Consider the reaction A + B + C → products. It has the rate law rate = k[A]  -1[B]3[C]2 Which of the following statements(s) is/are correct? i. The units of the rate constant are M -3 time-1. ii. The overall order of the reaction is 5. iii. Increasing the concentration of A by a factor of 3, B by a factor of 2 and C by a factor of 4 results in the overall rate increasing by a factor of 42.7. A. i only B. ii only C. iii only D. i and iii E. ii and iii
The rate law for the reaction H2O2 + 2H+ + 2l- → I2 + 2H2O is rate = k [H2O2] [I-]. the overall order of the reaction is (A) five (B) three (C) two (D) one
The reaction of peroxydisulfate ion (S2O8 2- ) with iodide ion (I - ) is: S2O8 2- (aq) + 3I - (aq) → 2SO4 2- (aq) + I3 - (aq) a.) What is the rate law?     b.) What is the rate constant?          
The reaction of peroxydisulfate ion (S2O82‐) with Iodide ion (I1‐) S2O82–+ 3 I –(aq) → 2SO42– + I3 From the data below calculate the rate constant for the reaction, k. A) 0.143 B) 0.0049 C) 0.0115 D) 0.061 E) 0.337  
Consider this reaction and its rate law. 3A + 2B --> products rate = k[A][B] What is the order with respect to A? What is the order with respect to B? What is the overall reaction order?
Give the characteristic of a first order reaction having only one reactant.  A. The rate of the reaction is not proportional to the concentration of the reactant. B. The rate of the reaction is proportional to the square of the concentration of the reactant. C. The rate of the reaction is proportional to the square root of the concentration of the reactant. D. The rate of the reaction is proportional to the natural logarithm of the concentration of the reactant.  E. The rate of the reaction is directly proportional to the concentration of the reactant. 
What is the overall order of the following reaction, given the rate law? 2NO(g) + H2(g) → N2(g) + 2H2O(g) Rate = k [NO]2[H2] A. 1st order B. 2nd order C. 3rd order D. 4th order E. 0th order
What are the units of k in the following rate law? A. Rate = k[X][Y]2 A) 1/Ms2 B) 1/M2s C) M2s D) M2/s E) 1/M3s
Given the following rate law, how does the rate of reaction change if the concentration of Y is doubled? A. Rate = k[X]2[Y]3 A) The rate of reaction will increase by a factor of 9. B) The rate of reaction will increase by a factor of 2. C) The rate of reaction will increase by a factor of 8. D) The rate of reaction will increase by a factor of 4. E) The rate of reaction will remain unchanged.
Determine the rate law and the value of k for the following reaction using the data providded. CO(g) + Cl2(g) → COCl2(g) [CO]i(M) [Cl2]i(M) Initial Rate (M-1s-1) 0.25         0.40             0.696 0.25         0.80             1.97 0.50         0.80             3.94 A) Rate = 11 M-3/2s-1[CO][Cl2]3/2 B) Rate = 36 M-1.8s-1[CO][Cl2]2.8 C) Rate = 17 M-2s-1[CO][Cl2]2 D) Rate = 4.4 M-1/2s-1[CO][Cl2]1/2 E) Rate = 18 M-3/2s-1[CO]2[Cl2]1/2  
Consult the table and find the rate constant of the reaction. A) 2.1 x 10-2 M-1 s-1 B) 2.1 x 10-1 M-1 s-1 C) 2.3 x 10-2 M-1 s-1 D) 1.4 x 10-1 M-1 s-1 E) 6.9 x 10-2 M-1 s-1
The reaction between ethyl bromide (C2H5Br) and hydroxide ion (OH -) in ethyl alcohol at 330 K is first order each in ethyl bromide and hydroxide ion. C2H5Br(alc) + OH -(alc) → C2H5OH(I) + Br -(alc) How would the rate of ethyl bromide change if the solution were diluted by adding an equal volume of pure ethyl alcohol to the solution.   a) no change b) decrease by a factor of four c) increase by a factor of four d) increase by a factor of two e) decrease by a factor of two
If the rate of a reaction increases by a factor of 9 when the concentration of reactant increases by a factor of 3, the order of the reaction (with respect to this reactant) is a) 2 b) 3 c) 9 d) 4 e) 1 
Given that the rate law for the production of water 2 H2 (g) +  O2 (g) → 2 H2O (l) is rate = k[H2]2[O2] –1, then the overall order of the reaction is  a) 1 b) 2 c) 3 d) –1 e) 0  
For the reaction 2A + B → products determine the rate law for the reaction given the following data:  Initial Concentration M,           Initial Rate, M·s–1   A          B 0.10       0.10                           2.0 x 10   –2 0.20       0.10                           8.0 x 10   –2 0.30       0.10                           1.8 x 10   –1 0.20       0.20                           8.0 x 10   –2 0.30       0.30                           1.8 x 10   –1 a) rate = k [A] b) rate = k [A][B] c) rate = k[A] [B] 0 d) rate = k[A]2 e) rate = k[B]2
When the reaction CH3Cl(g) + H2O(g) → CH3OH(g) + HCl(g) was studied, the tabulated data were obtained. Based on these data, what are the reaction orders? (A) CH3Cl: first order         H 2O: first order (B) CH3Cl: first order         H 2O: second order (C) CH3Cl: second order     H 2O: first order (D) CH3Cl: second order     H 2O: second order
The gas-phase reaction, A2 + B2 → 2AB, proceeds by bimolecular collisions between A2 and B2 molecules. If the concentrations of both A2 and B2 are doubled, the reaction rate will change by a factor of A) 1/2 B) √2 C) 2 D) 4
The following kinetic data was obtained for the reaction 2A + B → Products
Initial rate data for the reaction 2 H2 (g) + Cl2 (g) are given in the table. What is the rate law for this reaction? (A) rate k [Cl2]2 (B) rate = k [Cl2] (C) rate = k [H2] (D) rate = k [H2] [Cl2]
A kinetic study of the reaction 2 ClO2(aq) + 2 OH -(aq) → ClO2- (aq) + ClO3- (aq) +   H2O(l) yielded the data shown on the image. A.  What is the rate of appearance of the ClO3- in experiment 1 (Be sure to inlcude units in this and other answers.)   B. Determine the experimental rate law.   C. Determine the value of the rate constant  based on your answer to Part C. (Inlude units)