Solution Entropy: H2(g) Standard Values

[Big-Daddy]

Normally due to H⁺ being the reference state in solution, all 'standard molar' state variables and 'standard value of formation' state variables are 0 for it. But H₂(g) has a standard enthalpy of formation = 0 and standard molar entropy of 115 Jmol^-1K^-1. Then shouldn't ΔG°(298) for the reaction

2H⁺(aq) + 2e^- = H₂(g)

be -34,720 J and K = 1 * 10⁶, E°=+0.1799?

But I thought according to electrochemistry that E°=ΔG°=0 for this reaction and thus K=1.

 

[jbsteele]

Yes, the standard enthalpy of formation of H2(g) is 0 J/mol and the standard molar entropy is 115 J/mol·K. However, the standard free energy of formation of H2(g) is not 0 J/mol. It is actually -285.8 kJ/mol. Therefore, the standard Gibbs free energy of reaction (ΔG°) for the given reaction would be -285.8 kJ/mol and the equilibrium constant (K) would be 1 × 10⁶. The standard potential (E°) of the reaction would be +0.1799 V.