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Thermodynamic potentials

In thermodynamics, four different quantities, measured in units of energy, are called thermodynamic potentials:

where T = temperature, S = entropy, p = pressure, V = volume

Chemical reactions

Changes in these quantities are useful for assessing the degree to which a chemical reaction will proceed. The relevant quantity depends on the reaction conditions, as shown in the following table. (NB "Δ" denotes the change in a quantity.)

 Constant VConstant p
Constant SΔUΔH
Constant TΔFΔG

Most commonly one considers reactions at constant p and T, so the Gibbs free energy is the most useful potential in studies of chemical reactions.

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