the word "molar", not "specific", should always be used for this quantity. Definition The molar heat capacity of a substance, which may be denoted by cm, is the heat capacity C of a sample of the substance, divided by the amount (moles) n of the substance in the sample: cm where ΔQ is the amount of heat needed to raise the temperature of the sample by ΔT. Obviously, this parameter cannot be computed when n is not known or defined. Like the heat capacity of an object, the molar heat capacity of a substance may vary, sometimes substantially, depending on the starting temperature T of the sample and the pressure P applied to it. Therefore, it should be considered a function cm(P,T) of those two variables. These parameters are usually specified when giving the molar heat capacity of a substance. For example, "H2O: 75.338 J⋅K−1⋅mol−1 (25 °C, 101.325 kPa)" When not specified, published values of the molar heat capacity cm generally are valid for some standard conditions for temperature and pressure. However, the dependency of cm(P,T) on starting temperature and pressure can often be ignored in practical contexts, e.g. when working in narrow ranges of those variables. In those contexts one can usually omit the qualifier (P,T), and approximate the molar heat capacity by a constant cm suitable for those ranges. Since the molar heat capacity of a substance is the specific heat c times the molar mass of the substance M/N its numerical value is generally smaller than that of the specific heat. Paraffin wax, for example, has a specific heat of about but a molar heat capacity of about . The molar heat capacity is an "intensive" property of a substance, an intrinsic characteristic that does not depend on the size or shape of the amount in consideration. (The qualifier "specific" in front of an extensive property often indicates an intensive property derived from it.) Variations The injection of heat energy into a substance, besides raising its temperature, usually causes an increase in its volume and/or its pressure, depending on how the sample is confined. The choice made about the latter affects the measured molar heat capacity, even for the same starting pressure P and starting temperature T. Two particular choices are widely used: If the pressure is kept constant (for instance, at the ambient atmospheric pressure), and the sample is allowed to expand, the expansion generates work