Q1(d). Composition change and non-expansion work

Answer in brief

At constant T,p, the maximum reversible non-expansion work delivered is -ΔG; composition changes enter through chemical potentials.

Key points

• The fundamental relation is dG=-S dT+V dp+Σᵢμᵢ dnᵢ. For a reaction, dnᵢ=νᵢ dξ, so at fixed T,p, dG=ΔᵣG dξ with ΔᵣG=Σᵢνᵢμᵢ.
• For reversible operation, the non-expansion work done on the system is δ w_(nonPV,rev)=dG at constant T,p.
• For example, a galvanic cell converts chemical composition change into electrical work: ΔᵣG=-nFE. Irreversibility reduces the useful work obtained for the same endpoint states.