# Hydrogen gas is being considered as a fuel for automobiles. There are many chemical means for producing hydrogen gas from water. One of these reactions is C ( s ) + H 2 O ( g ) → CO ( g ) + H 2 ( g ) In this case the form of carbon used is graphite. a. Calculate ∆ H° and ∆ S° for this reaction using data from Appendix 4. b. At what temperature is ∆ G° = zero for this reaction? Assume ∆ H° and ∆ S° do not depend on temperature.

### Chemistry: An Atoms First Approach

2nd Edition
Steven S. Zumdahl + 1 other
Publisher: Cengage Learning
ISBN: 9781305079243

Chapter
Section

### Chemistry: An Atoms First Approach

2nd Edition
Steven S. Zumdahl + 1 other
Publisher: Cengage Learning
ISBN: 9781305079243
Chapter 19, Problem 87CWP
Textbook Problem
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## Hydrogen gas is being considered as a fuel for automobiles. There are many chemical means for producing hydrogen gas from water. One of these reactions is C ( s ) + H 2 O ( g ) → CO ( g ) + H 2 ( g ) In this case the form of carbon used is graphite.a. Calculate ∆H° and ∆S° for this reaction using data from Appendix 4.b. At what temperature is ∆G° = zero for this reaction? Assume ∆H° and ∆S° do not depend on temperature.

(a)

Interpretation Introduction

Interpretation: Standard enthalpy of the reaction and change in standard entropy of the given reaction are to be determined and the temperature at which the change in standard Gibb’s energy is zero, is to be calculated.

Concept introduction: The standard enthalpy of the reaction is calculated by the formula,

ΔHreaction=ΔHformation(product)ΔHformation(reactant)

The change in standard Gipp’s free energy of the reaction is calculated as,

ΔG=ΔHTΔS

To determine: Standard enthalpy of the reaction and change in standard entropy of the given reaction.

### Explanation of Solution

Hydrogen gas is produced by reacting graphite with water.

C(s)+H2O(g)CO(g)+H2(g)

The standard enthalpy of formation of H2O(g) is 242kJ/mol .

The standard enthalpy of formation of CO(g) is 110.5kJ/mol .

The standard enthalpy of formation of C(s) and H2(g) is zero since the standard enthalpy of formation of free elements in their standard state is zero.

The standard enthalpy of the reaction is calculated by the formula,

ΔHreaction=ΔHformation(product)ΔHformation(reactant)

Therefore, the above equation becomes,

ΔHreaction=ΔHformation(CO(g))ΔHformation(H2O(g))

Substitute the value of ΔHformation(CO(g)) and ΔHformation(H2O(g)) in the above equation.

ΔHreaction=(110.5kJ/mol)(242kJ/mol)=110.5kJ/mol+242kJ/mol=+131.5kJ/mol_

Therefore, the standard enthalpy of the reaction is +131.5kJ/mol .

The standard entropy of H2O(g) is 189J/Kmol .

The standard entropy of CO(g) is 198J/Kmol

(b)

Interpretation Introduction

Interpretation: Standard enthalpy of the reaction and change in standard entropy of the given reaction are to be determined and the temperature at which the change in standard Gibb’s energy is zero, is to be calculated.

Concept introduction: The standard enthalpy of the reaction is calculated by the formula,

ΔHreaction=ΔHformation(product)ΔHformation(reactant)

The change in standard Gipp’s free energy of the reaction is calculated as,

ΔG=ΔHTΔS

To determine: The temperature at which the change in standard Gipp’s energy of the given reaction is zero.

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