To describe dynamics of the systems that obey the generalized mass action law, one has to represent the activities as functions of the concentrations c j and temperature. For this purpose, use the representation of the activity through the chemical potential: a i = exp ⁡ ⁡ ( μ μ i − − μ μ i ⊖ ⊖ R T ) where μ i is the chemical potential of the species under the conditions of interest, ⁠ μ μ i ⊖ ⊖ ⁠ is the chemical potential of that species in the chosen standard state, R is the gas constant and T is the thermodynamic temperature. The chemical potential can be represented as a function of c and T, where c is the vector of concentrations with components c j. For the ideal systems, μ μ i = R T ln ⁡ ⁡ c i + μ μ i ⊖ ⊖ and a j = c j : the activity is the concentration and the generalized mass action law is the usual law of mass action.