Ch.6 - Thermochemistry WorksheetSee 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

Solution: Consider these reactions, where M represents a generic metal. 1.  2M (s) + 6HCl (aq)  →  2MCl3 (aq) + 3H2 (g)                 ΔH1 = -579.0 kJ 2. HCl (g) → HCl (aq)                                                         ΔH2 = -74.8 kJ 3. H2 (g) + Cl2 (g) → 2HCl (g)                                            ΔH3 = -1845.0 kJ 4. MCl3 (s) → MCl3 (aq)                                                     ΔH4 = -141.0 kJ Use the following information above to determine the enthalpy (kJ) of the following reaction. 2 M(s) +  3Cl2 (g) → 2 MCl(s)

Solution: Consider these reactions, where M represents a generic metal.1.  2M (s) + 6HCl (aq)  →  2MCl3 (aq) + 3H2 (g)                 ΔH1 = -579.0 kJ2. HCl (g) → HCl (aq)                                      

Problem

Consider these reactions, where M represents a generic metal.

1.  2M (s) + 6HCl (aq)  →  2MCl3 (aq) + 3H2 (g)                 ΔH1 = -579.0 kJ
2. HCl (g) → HCl (aq)                                                         ΔH2 = -74.8 kJ
3. H2 (g) + Cl2 (g) → 2HCl (g)                                            ΔH3 = -1845.0 kJ
4. MCl3 (s) → MCl3 (aq)                                                     ΔH4 = -141.0 kJ

Use the following information above to determine the enthalpy (kJ) of the following reaction.

2 M(s) +  3Cl2 (g) → 2 MCl(s)


Solution

We’re being asked to determine the enthalpy change (ΔHrxn) for the chemical reaction:


2 M(s) + 3 Cl2(g)  2 MCl3(s)


We can use Hess’s Law to determine the enthalpy change of the overall reaction from the given reactions:


1. 2 M(s) + 6 HCl(aq)  2 MCl3(aq) + 3 H2(g)                 ΔH1 = –579.0 kJ

2. HCl(g)  HCl(aq)                                                         ΔH2 = –74.8 kJ

3. H2(g) + Cl2(g)  2 HCl(g)                                             ΔH3 = –1845.0 kJ

4. MCl3(s)  MCl3(aq)                                                      ΔH4 = –141.0 kJ


We now need to find a combination of reactions that when added up, gives us the overall reaction.


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