Question

The most important commercial process for generating hydrogen gas is the water-gas shift reaction:
CH₄(g) + H₂O(g) → CO(g) + 3H₂(g)
Use tabulated thermodynamic data to find ΔG° for this reaction at the standard temperature of 25°C.
1.423×10² kJ

Calculate ΔG°₁₀₀₀ for this process when it occurs at 1000 K
.

Answer 1

    CH₄(g) + H₂O(g) → CO(g) + 3H₂(g)

from standard data

DHrxn = (DH0fCO + 3*DH0fH2) - (1*DH0fCH4+1*DH0fH2O)

             = (-110.5 + 3*0) - (-74.8 -241.8)

             = 206.1 kj

DSrxn = (S0fCO + 3*S0fH2) - (1*S0fCH4+1*S0fH2O)

             = (197.9 +3*130.59) - (186.27+188.72)

              = 214.68 j/mol.k

DG = DH - TDS

    at T = 25 C = 298 k

DG = 209.1 - (298*214.68*10^-3) = 145.12 kj

at T = 1000 k

DG = 209.1 - (1000*214.68*10^-3)   = -5.58 kj