Isochoric process

An isochoric process is exemplified by the heating or the cooling of the contents of a sealed, inelastic container: The thermodynamic process is the addition or removal of heat; the isolation of the contents of the container establishes the closed system; and the inability of the container to deform imposes the constant-volume condition.

An isochoric thermodynamic quasi-static process is characterized by constant volume, i.e., ΔV = 0.

The sign convention is such that positive work is performed by the system on the environment.

[1] For a reversible process, the first law of thermodynamics gives the change in the system's internal energy:

Using the definition of specific heat capacity at constant volume, cv = (dQ/dT)/m, where m is the mass of the gas, we get

On a pressure volume diagram, an isochoric process appears as a straight vertical line.

Its thermodynamic conjugate, an isobaric process would appear as a straight horizontal line.

If an ideal gas is used in an isochoric process, and the quantity of gas stays constant, then the increase in energy is proportional to an increase in temperature and pressure.

The ideal Otto cycle is an example of an isochoric process when it is assumed that the burning of the gasoline-air mixture in an internal combustion engine car is instantaneous.

There is an increase in the temperature and the pressure of the gas inside the cylinder while the volume remains the same.

The noun "isochor" and the adjective "isochoric" are derived from the Greek words ἴσος (isos) meaning "equal", and χῶρος (khôros) meaning "space."