The specific heat of a substance may be defined as the amount of heat required to raise the temperature of unit mass of the substance through one degree. It depends on the nature of the substance and its temperature.
If an amount of heat ∆Q is needed to raise the temperature of M mass of a substance through ∆T, then it is called specific heat capacity.
The CGS unit of specific heat is cal g-1 ℃-1 and SI units is J kg-1 K-1.
Molar specific heat: If the amount of substance is specified in terms of moles μ, instead of mass m in kg, we can define heat capacity per mole of the substance by
where C is known as molar specific heat capacity of the substance. Like S, C also depends on the nature of the substance and its temperature
SI units of molar specific heat capacity are J mol-1 K-1.
If the gas is held under constant pressure during the heat transfer, then it is called the molar specific heat capacity at constant pressure and is denoted by Cp.
On the other hand, if the volume of the gas is maintained during the heat transfer, then the corresponding molar specific heat capacity is called molar specific heat capacity at constant volume and is denoted by CV.