Nomenclature 1 Nomenclature 2 Heat capacity at constant V, C V {\displaystyle C_{V}} , or constant P, C P {\displaystyle C_{P}} . Ideal-gas law p V = n R T {\displaystyle pV=nRT} and C p − C V = n R {\displaystyle C_{p}-C_{V}=nR} Calorically perfect Perfect Constant Yes Thermally perfect Semi-perfect T-dependent Yes Ideal May be T and/or p-dependent Yes Imperfect T and p-dependent No