A process for manufacturing acetylene involves the dehydrogenation of ethane ove
ID: 474810 • Letter: A
Question
A process for manufacturing acetylene involves the dehydrogenation of ethane over a newly discovered catalyst. The process will operate at 1 bar and a yet unspecified temperature. The only reaction is thought to occur entirely in the gas phase: . The following thermochemical data is available:
Component
Go298 (kJ/mole)
Ho298 (kJ/mole)
Ethane
-32.9
-84.7
Acetylene
209.3
226.9
Please answer the following:
What is the standard Gibbs free energy change at 25oC for this reaction?
What is the standard enthalpy change of reaction at 25oC?
What is the equilibrium constant for this reaction at 25oC?
Assuming the standard enthalpy change is independent of temperature what is the equilibrium constant for this reaction at 827oC?
If we supply pure ethane at 827oC to the reactor at 1 bar, and if equilibrium is obtained, what is the composition of the final product mixture. Assume the reactor operates isothermally at these conditions.
Component
Go298 (kJ/mole)
Ho298 (kJ/mole)
Ethane
-32.9
-84.7
Acetylene
209.3
226.9
Explanation / Answer
C2H6 ------------------------>C2H2 + 2 H2
1)
Gibbs free energy change = Go products - Go reactants
= (209.3 + 2 x 0 ) - (-32.9)
= 242.2 kJ / mol
standard enthalpy change = Ho products - Ho reactants
= (226.9 + 2 x 0 ) - (-84.7)
= 311.6 kJ / mol
3) What is the equilibrium constant for this reaction at 25oC?
Go = - RT ln Keq
242.2 = -8.314 x 10^-3 x 298 x ln Keq
ln Keq = -97.76
Keq = 3.49 x 10^-43
equilibrium constant = 3.49 x 10^-43
4) Assuming the standard enthalpy change is independent of temperature what is the equilibrium constant for this reaction at 827oC?
T = 827 + 273 = 1100 K
Go = - RT ln Keq
242.2 = -8.314 x 10^-3 x 1100 x ln Keq
ln Keq = -26.48
Keq = 3.16 x 10^-12
equilibrium constant = 3.16 x 10^-12
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