= Molar Gibbs free energy
{title2=$G_m$}
The <molar Gibbs free energy> is the <Gibbs free energy> per <amount of substance>, $G_m=G/n$, with units $\mathrm{J\,mol^{-1}}$. For a homogeneous pure substance, extensivity gives $G=n\mu$, so $G_m$ equals its <chemical potential> $\mu$.
For a <mixture>, $G/n$ is an average over the components; the separate <chemical potentials> are the partial derivatives $\mu_i=(\partial G/\partial n_i)_{T,p,n_{j\ne i}}$. Equality of a component's <chemical potential> in two phases is a condition for <phase equilibrium>. This explains why comparing molar free energies predicts which phase of a pure substance is stable at specified <temperature> and <pressure>.
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