This Demonstration shows a plot of the Gibbs free energy for the equilibrium between nitrogen dioxide and dinitrogen tetroxide () as a function of , the extent of reaction. The reaction proceeds until the Gibbs function reaches a minimum, at the value . The equilibrium constant of the reaction can be computed from the value of using the equation , where , the total moles present at equilibrium, is equal to . Similarly, because at equilibrium , we find that .