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a process that occurs in a physical system at constant volume.
In gases and liquids, isochoric processes can be brought about easily, it being necessary only to put the liquid or gas in a hermetic vessel that does not change volume. In an isochoric process no mechanical work is performed that is associated with a change in the volume of the body; the change in the internal energy of the body takes place only through the absorption or release of heat. The pressure changes with changes in the temperature of the gas (or liquid). During an isochoric process the pressure of an ideal gas is proportional to the temperature. This relationship is not observed for a nonideal gas, since part of the heat conveyed to the gas is used to increase the particles’ interaction energy. Technically, it is much more difficult to carry out an isochoric process in a solid. Because of the low compressibility of a solid, virtually any isothermic process in a solid is nearly isochoric, even to pressures on the order of tens of kilobars (~ 109 newtons per sq m).