In an irreversible chemical reaction, the maximum work that can be done is equal to the change in Gibbs free energy G of the reaction. Gibbs free energy is a thermodynamic potential that measures the maximum reversible work that can be done by a system at constant temperature and pressure.The Gibbs free energy change G can be calculated using the following equation:G = H - TSwhere H is the change in enthalpy heat content of the reaction, T is the absolute temperature in Kelvin, and S is the change in entropy disorder of the reaction.For an irreversible reaction, the actual work done will be less than the maximum work G due to inefficiencies and energy losses. However, the maximum work that can be done by the reaction is still represented by the change in Gibbs free energy G .