Consider the water-gas-shift reaction:
H2(g) + CO2(g) †’ H2O(g) + CO(g)
At high temperatures and low to moderate pressures the reacting species form an ideal- gas mixture. By Eq. (11.27):

When the Gibbs energies of the elements in their standard states are set equal to zero, Gi = AGofi for each species, and then:

At the beginning of Sec. 13.2 we noted that Eq. (14.68) is a criterion of equilibrium. Applied to the water-gas-shift reaction with the understanding that T and P arc constant, this equation becomes:

Here, however, dn/dÉ› = 0. The equilibrium criterion therefore becomes
dG/ dÉ› = 0
Once the yi are eliminated in favor of e, Eq. (A) relates G to É›. Data for AGofi ', for the compounds of interest are given with Ex. 13.13. For a temperature of 1,000 K (the reaction is unaffected by P) and for a feed of 1 mol H2 and 1 mol CO2:
(a) Determine the equilibrium value of e by application of Eq. (B).
(b) Plot G vs. É› indicating the location of the equilibrium value of e determined in

Transcribed Image Text:

dG dn dede