Chemical reactions do not go to completion. Rather, a dynamical equilibrium between reactants and products is established. This equilibrium state can be derived from the law of mass action as contained in the equilibrium constant.
By careful consideration of the thermodynamics of gas phase processes, the change in the Gibbs free energy during a reaction can be related to the equilibrium constant.
To prepare for this lecture, we suggest that you read sections 9-1 and 9-2 of Oxtoby.
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