The amount of heat required to raise the temperature of a substance by 1 degree Kelvin is called the heat capacity of the substance. For gases, if the pressure remains constant during the heating process, the heat capacity is represented by the symbol CP, while if the volume remains constant the symbol used is CV. The corresponding symbols for molar heat capacity (i.e., the heat capacity of 1 mol of the substance) are cP for constant pressure and cV for constant volume.