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: From the enthalpies of reaction2 C(s) + O2(g) → 2CO(g)                               ΔH = -221.0 kJ2C(s) + O2(g) + 4H2(g) → 2CH3OH(g)       ΔH = -402.4 kJcalculate ΔH for the reaction:CH3OH(g) → CO(g)

Problem

From the enthalpies of reaction

2 C(s) + O2(g) → 2CO(g)                               ΔH = -221.0 kJ
2C(s) + O2(g) + 4H2(g) → 2CH3OH(g)       ΔH = -402.4 kJ

calculate ΔH for the reaction:

CH3OH(g) → CO(g) + 2H2(g) 

a) -90.7 kJ      

b) 90.7 kJ       

c) -623.4 kJ    

d) 180.7 kJ     

e) 623.4 kJ

Solution
  • Apply Hess’s Law to determine the ΔH of the overall reaction where we have to get the sum of ΔH of the elementary reactions given
  • The overall reaction appears to be:

CH3OH (g) → CO (g) + 2H2 (g) 

  • And the elementary reactions are:

2 C(s) + O(g) → 2CO (g)                               ΔH = -221.0 kJ
2C(s) + O2 (g) + 4 H2 (g) → 2CH3OH (g)      ΔH = -402.4 kJ

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