Does pH affect Gibbs free energy?

1 Answer
Truong-Son N.
Apr 21, 2018

Sometimes...

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)#

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