The chemical potential $\mu_{i}$ of component i in a one-phase system is given by: \begin{equation} \mu_i =\left(\frac{\partial G}{\partial n_i}\right)_ {T,P,n_{j\neq i}} \end{equation} The chemical potential of a substance i in phase $\alpha$ is a state function that depends on temperature, pressure, and phase composition, $ µ_{i}^{\alpha} = µ_{i}^{\alpha}(T^{\alpha}, P^{\alpha}, x_{1}^{\alpha}, x_{2} ^{\alpha}...)$

For a pure substance the chemical potential coincides with the molar Gibbs free energy $\mu_{i}=\left(\frac{\partial G}{\partial n_i}\right)_{T,P}=\bar{ G}_i$