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: Given:1. A → 2B, ΔH2. B → C + D, ΔH2 3. E → 2D, ΔH3ΔH of A → 2C + E is:A. ΔH1 + 2ΔH2 – ΔH3 B. ΔH2 - ΔH2 – ΔH3 C. ΔH3 – ΔH3 D. ΔH1 + 2ΔH1 – ΔH2 E. None of the above

Problem

Given:

1. A → 2B, ΔH

2. B → C + D, ΔH2 

3. E → 2D, ΔH3

ΔH of A → 2C + E is:

A. ΔH1 + 2ΔH2 – ΔH3 

B. ΔH2 - ΔH2 – ΔH3 

C. ΔH3 – ΔH3 

D. ΔH1 + 2ΔH1 – ΔH2 

E. None of the above

Solution

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


 A → 2C + E


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


1. A → 2B                                         ΔH1 

2. B → C + D                                    ΔH2 

3. E → 2D                                         ΔH3


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


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