Question

Does pH affect Gibbs free energy?

Answer 1

Sometimes...

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It does if the reaction involves an acid... The Gibbs' free energy is a function of the reaction quotient:

`DeltaG = DeltaG^@ + RTlnQ`

and if `Q` is a function of `["H"_3"O"^(+)]`, then `DeltaG = DeltaG(10^(-"pH"))`. Some examples are...

`"HC"_2"H"_3"O"_2(aq) + "H"_2"O"(l) rightleftharpoons "C"_2"H"_3"O"_2^(-)(aq) + "H"_3"O"^(+)(aq)`, `K_a = 1.8 xx 10^(-5)`

`"NH"_3(aq) + "H"_2"O"(l) rightleftharpoons "NH"_4^(+)(aq) + "OH"^(-)(aq)`, `K_b = 1.8 xx 10^(-5)`