(a)
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,
ΔH∘reaction=ΔH∘formation(product)−ΔH∘formation(reactant)
The change in standard Gipp’s free energy of the reaction is calculated as,
ΔG∘=ΔH∘−TΔS∘
To determine: Standard enthalpy of the reaction and change in standard entropy of the given reaction.
(a)

Answer to Problem 95CWP
Standard enthalpy of the reaction and change in standard entropy of the given reaction is +131.5 kJ/mol_ and 134 J/K⋅mol_, respectively.
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 −242 kJ/mol.
The standard enthalpy of formation of CO(g) is −110.5 kJ/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,
ΔH∘reaction=ΔH∘formation(product)−ΔH∘formation(reactant)
Therefore, the above equation becomes,
ΔH∘reaction=ΔH∘formation(CO(g))−ΔH∘formation(H2O(g))
Substitute the value of ΔH∘formation(CO(g)) and ΔH∘formation(H2O(g)) in the above equation.
ΔH∘reaction=(−110.5 kJ/mol)−(−242 kJ/mol)=−110.5 kJ/mol+242 kJ/mol=+131.5 kJ/mol_
Therefore, the standard enthalpy of the reaction is +131.5 kJ/mol.
The standard entropy of H2O(g) is 189 J/K⋅mol.
The standard entropy of CO(g) is 198 J/K⋅mol.
The standard entropy of C(s) is 6 J/K⋅mol.
The standard entropy of H2(g) is 131 J/K⋅mol.
The standard entropy change of the reaction is calculated by the formula,
ΔS∘reaction=S∘(product)−S∘(reactant)
Therefore, the above equation becomes,
ΔS∘reaction=[S∘(CO(g))+S∘(H2(g))]−[S∘(H2O(g))+S∘(C(s))]
Substitute the value of S∘(CO(g)), S∘(H2(g)), S∘(H2O(g)) and S∘(C(s)) in the above equation.
ΔS∘reaction=[198 J/K⋅mol+131 J/K⋅mol]−[189 J/K⋅mol+6 J/K⋅mol]=329 J/K⋅mol−195 J/K⋅mol=134 J/K⋅mol_
Therefore, the standard entropy change of the reaction is 134 J/K⋅mol_.
(b)
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,
ΔH∘reaction=ΔH∘formation(product)−ΔH∘formation(reactant)
The change in standard Gipp’s free energy of the reaction is calculated as,
ΔG∘=ΔH∘−TΔS∘
To determine: The temperature at which the change in standard Gipp’s energy of the given reaction is zero.
(b)

Answer to Problem 95CWP
The temperature at which the change in standard Gipp’s energy of the given reaction is zero is 981.3 K_
Explanation of Solution
Given
The change in standard Gipp’s energy of the given reaction is zero.
Standard enthalpy of the reaction and change in standard entropy of the given reaction is +131.5 kJ/mol and 134 J/K⋅mol, respectively.
The change in standard Gipp’s free energy of the reaction is calculated as,
ΔG∘=ΔH∘−TΔS∘
Substitute the value of ΔG∘, ΔH∘ and ΔS∘ in the above equation.
0=+131.5×103 J/mol−T×134 J/K⋅molT×134 J/K⋅mol=131.5×103 J/molT=131.5×103 J/mol134 J/K⋅mol=981.3 K_
Therefore, the temperature at which the change in standard Gipp’s energy of the given reaction is zero is 981.3 K_
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