Chemistry: An Atoms-Focused Approach
Chemistry: An Atoms-Focused Approach
14th Edition
ISBN: 9780393912340
Author: Thomas R. Gilbert, Rein V. Kirss, Natalie Foster
Publisher: W. W. Norton & Company
Question
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Chapter 12, Problem 12.69QA
Interpretation Introduction

To:

a) Calculate Grxn0 for the “steam-methane reforming” reaction using appropriate Gf0 values from Appendix 4.

b) Calculate Grxn0 for the “water-gas shift” reaction using appropriate Gf0 values from Appendix 4.

c) Write an overall (combined) chemical reaction from the first two given reactions to produce hydrogen and carbon dioxide.

d) Calculate the Grxn0 value of the overall reaction and tell if it is spontaneous or not.

Expert Solution & Answer
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Answer to Problem 12.69QA

Solution:

a) Calculated Grxn0 for the “steam-methane reforming” reaction is 142.2  kJ

b) Calculated Grxn0  for the “water-gas shift” reaction is -28.6 kJ

c) Overall (combined) chemical reaction from the first two given reactions is

 CH4g+2H2O gCO2g+4H2(g)

d) Calculated the Grxn0 value of the overall reaction is 113.6 kJ and the reaction is not spontaneous.

Explanation of Solution

1) Concept:

We can use the concept second law of thermodynamics and use the expressions of standard entropy, standard enthalpy and standard Gibb’s free energy to calculate each.

2) Formulae:

i.

Grxn0= nproductsGf products0-  nreactantsGf reactants0 

ii.

Hrxn0= nproductsHf products0-  nreactantsHf reactants0 

iii.

Srxn0= nproductsSproducts0-  nreactantsSreactants0 

iv.

Grxn0= Hrxn0-TSrxn0

3) Given:

i. A steam-methane reforming reaction is given as: CH4g+H2O gCOg+3H2(g)

ii. A water-gas shift reaction equation is given as: COg+H2OgCO2g+H2(g)

iii.

Hf0(kJ/mol) S(J(mol ×K)) Gf0(kJ/mol)
CH4(g) -74.8 186.2 -50.8
H2O (g) -241.8 69.9 -228.6
CO (g) -110.5 197.7 -137.2
H2(g) 0.0 130.6 0.0
CO2(g) -393.5 213.8 -394.4

4) Calculations:

a) Grxn0 for the “steam-methane reforming” reaction:

CH4g+H2O gCOg+3H2(g)

The steam-methane reforming reaction consumes 1 mole of methane and water each and produce 1 mole of carbon monoxide and 3 moles of hydrogen gas. Multiplying the Gf0 values by the appropriate numbers of moles and subtracting the sum of the reactants values from the sum of the product values given by the equation below will yield the value for  Grxn0.

Grxn0= nproductsGf products0-  nreactantsGf reactants0 

Grxn0= 1 mol×-137.2kJmol+3 mol×0.0kJmol-1 mol×-50.8kJmol+1 mol×-228.6kJmol

Grxn0=-137.2-+279.4

Grxn0 = 142.2  kJ

b) Grxn0 for the “steam-methane reforming” reaction:

COg+H2OgCO2g+H2(g)

The water-gas shift reaction consumes 1 mole of carbon monoxide and water each and produce 1 mole of carbon dioxide and 1 moles of hydrogen gas. Multiplying the Gf0 values by the appropriate numbers of moles and subtracting the sum of the reactants values from the sum of the product values given by the equation below will yield the value for  Grxn0.

Grxn0= nproductsGf products0-  nreactantsGf reactants0 

Grxn0= 1 mol×-394.4kJmol+1 mol×0.0kJmol-1 mol-137.2kJmol+1 mol×-228.6kJmol

Grxn0=-394.4--365.8

Grxn0 = -28.6 kJ

c) Overall reaction by combining the two given equations is:

CH4g+H2O gCOg+3H2(g)

+

COg+H2OgCO2g+H2(g)

CH4g+2H2O gCO2g+4H2(g)

d) Grxn0 for the overall (combined) reaction above is:

The overall reaction is:

CH4g+2H2O gCO2g+4H2(g)

The above reaction consumes 1 mole of methane gas and 1 mole of water vapor producing 1 mole of carbon dioxide and 4 moles of hydrogen gas. Multiplying the Gf0 values by the appropriate numbers of moles and subtracting the sum of the reactants values from the sum of the product values given by the equation below will yield the value for  Grxn0.

Grxn0= nproductsGf products0-  nreactantsGf reactants0 

Grxn0= 1 mol×-394.4kJmol+4 mol×0.0kJmol-1 mol-50.8kJmol+2 mol×-228.6kJmol

Grxn0=-394.4--508

Grxn0 = 113.6 kJ

The deltaG reaction Grxn0 is a positive value. This suggests that the reaction is non-spontaneous.

Conclusion:

a) Calculated Grxn0 for the “steam-methane reforming” reaction is 142.2  kJ

b) Calculated Grxn0  for the “water-gas shift” reaction is -28.6 kJ

c) Overall (combined) chemical reaction from the first two given reactions is

CH4g+2H2O gCO2g+4H2(g)

d) Calculated the Grxn0 value of the overall reaction is 113.6 kJ and the reaction is not spontaneous.

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Chapter 12 Solutions

Chemistry: An Atoms-Focused Approach

Ch. 12 - Prob. 12.13QACh. 12 - Prob. 12.14QACh. 12 - Prob. 12.15QACh. 12 - Prob. 12.16QACh. 12 - Prob. 12.17QACh. 12 - Prob. 12.18QACh. 12 - Prob. 12.19QACh. 12 - Prob. 12.20QACh. 12 - Prob. 12.21QACh. 12 - Prob. 12.22QACh. 12 - Prob. 12.23QACh. 12 - Prob. 12.24QACh. 12 - Prob. 12.25QACh. 12 - Prob. 12.26QACh. 12 - Prob. 12.27QACh. 12 - Prob. 12.28QACh. 12 - Prob. 12.29QACh. 12 - Prob. 12.30QACh. 12 - Prob. 12.31QACh. 12 - Prob. 12.32QACh. 12 - Prob. 12.33QACh. 12 - Prob. 12.34QACh. 12 - Prob. 12.35QACh. 12 - Prob. 12.36QACh. 12 - Prob. 12.37QACh. 12 - Prob. 12.38QACh. 12 - Prob. 12.39QACh. 12 - Prob. 12.40QACh. 12 - Prob. 12.41QACh. 12 - Prob. 12.42QACh. 12 - Prob. 12.43QACh. 12 - Prob. 12.44QACh. 12 - Prob. 12.45QACh. 12 - Prob. 12.46QACh. 12 - Prob. 12.47QACh. 12 - Prob. 12.48QACh. 12 - Prob. 12.49QACh. 12 - Prob. 12.50QACh. 12 - Prob. 12.51QACh. 12 - Prob. 12.52QACh. 12 - Prob. 12.53QACh. 12 - Prob. 12.54QACh. 12 - Prob. 12.55QACh. 12 - Prob. 12.56QACh. 12 - Prob. 12.57QACh. 12 - Prob. 12.58QACh. 12 - Prob. 12.59QACh. 12 - Prob. 12.60QACh. 12 - Prob. 12.61QACh. 12 - Prob. 12.62QACh. 12 - Prob. 12.63QACh. 12 - Prob. 12.64QACh. 12 - Prob. 12.65QACh. 12 - Prob. 12.66QACh. 12 - Prob. 12.67QACh. 12 - Prob. 12.68QACh. 12 - Prob. 12.69QACh. 12 - Prob. 12.70QACh. 12 - Prob. 12.71QACh. 12 - Prob. 12.72QACh. 12 - Prob. 12.73QACh. 12 - Prob. 12.74QACh. 12 - Prob. 12.75QACh. 12 - Prob. 12.76QACh. 12 - Prob. 12.77QACh. 12 - Prob. 12.78QACh. 12 - Prob. 12.79QACh. 12 - Prob. 12.80QACh. 12 - Prob. 12.81QACh. 12 - Prob. 12.82QACh. 12 - Prob. 12.83QACh. 12 - Prob. 12.84QACh. 12 - Prob. 12.85QACh. 12 - Prob. 12.86QA
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