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: (i) Consider this reactionC2H5OH + 3O2 → 2CO2 + 3H2O Change in Heat = -1370 kJ/molWhat is the enthalpy for this reaction reversed?Reaction reversed: 2CO2 + 3H2O → C2H5OH + 3O2Change in Heat = ? kJ/mol

Problem

(i) Consider this reaction
C2H5OH + 3O2 → 2CO2 + 3H2O Change in Heat = -1370 kJ/mol

What is the enthalpy for this reaction reversed?

Reaction reversed: 2CO2 + 3H2O → C2H5OH + 3O2
Change in Heat = ? kJ/mol

(ii) Calculate the enthalpy of the reaction
2NO(g) + O2(g) → 2NO2(g)
Given the following reactions and enthalpies of formation:
½ N2(g) + O2(g) → NO2(g) Change in Heat a = 33.2 KJ
½ N2(g) + ½ O2 (g) → NO(g) Change in Heat b = 90.2 KJ
Express your answer numerically in kilojoules.

Change in Heat = ? kJ/mol

Please show all your steps and explain why you did what.

Solution

(i) Consider this reaction


C2H5OH + 3O2 → 2CO2 + 3H2O  Change in Heat = -1370 kJ/mol


When we reverse a reaction, we get the same numerical value for the enthalpy change except that we change the sign. 


We initially have a negative charge so we make it positive for the reverse reaction. 


Reaction reversed: 2CO2 + 3H2O → C2H5OH + 3O2
Change in Heat = + 1370 kJ/mol 

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