A measure of the reversible amount of this quantity at constant temperature and volume is the Helmholtz free energy.
In a Carnot engine, entering heat times one minus the ratio of the temperatures of the resevoirs is equal to this quantity. It's not a change in volume, but an isochoric process has a value of zero for this quantity. A measure of the reversible amount of this quantity at constant temperature and volume is the Helmholtz free energy. Taking an integral on a PV diagram gives this quantity. In thermodynamics, change in internal energy is equal to heat added plus this quantity. Identify this concept for which the SI unit is Joules and can be calculated by multiplying force and distance.
In a Carnot engine, entering heat times one minus the ratio of the temperatures of the resevoirs is equal to this quantity.
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