cpcv

CpCv is not a standard standalone term in thermodynamics, but it is commonly used informally to refer to the two related heat capacities: Cp, the molar (or specific) heat capacity at constant pressure, and Cv, the molar (or specific) heat capacity at constant volume. In many discussions, CpCv is used to denote the relationship between these two properties, or simply to reference both Cp and Cv together.

The ratio gamma = Cp/Cv, also called the heat capacity ratio or adiabatic index, is a central quantity in thermodynamics. It characterizes the response of a gas to compression or expansion and appears in formulas for the speed of sound and for adiabatic processes. For an ideal gas, Cp − Cv = R, where R is the gas constant, and Cp/Cv = gamma, which depends on the molecule’s degrees of freedom. Cp and Cv can be expressed in molar units (J/mol·K) or specific units (J/kg·K), and they can be determined experimentally by calorimetry or inferred from thermodynamic relations.

In solids and liquids, the difference Cp − Cv is smaller than for gases, but both quantities still vary with temperature and phase. Cp and Cv are used to model energy storage, heat transfer, and material behavior in engineering and scientific contexts. When encountered, CpCv should be interpreted from context, as it does not denote a single universal quantity on its own.