heat capacity of a body made of the material in question, is the mass of the body, is the volume of the body, and is the density of the material. For gases, and also for other materials under high pressures, there is need to distinguish between different boundary conditions for the processes under consideration (since values differ significantly between different conditions). Typical processes for which a heat capacity may be defined include isobaric (constant pressure, ) or isochoric (constant volume, ) processes. The corresponding specific heat capacities are expressed as A related parameter to is , the volumetric heat capacity. In engineering practice, for solids or liquids often signifies a volumetric heat capacity, rather than a constant-volume one. In such cases, the mass-specific heat capacity is often explicitly written with the subscript , as . Of course, from the above relationships, for solids one writes For pure homogeneous chemical compounds with established molecular or molar mass or a molar quantity is established, heat capacity as an intensive property can be expressed on a per mole basis instead of a per mass basis by the following equations analogous to the per mass equations: where n = number of moles in the body or thermodynamic system. One may refer to such a per mole quantity as molar heat capacity to distinguish it from specific heat capacity on a per-mass basis. Polytropic heat capacity The polytropic heat capacity is calculated at processes if all the thermodynamic properties (pressure, volume, temperature) change The most important polytropic processes run between the adiabatic and the isotherm functions, the polytropic index is between 1 and the adiabatic exponent (γ or κ) Dimensionless heat capacity The dimensionless heat capacity of a material is where C is the heat capacity of a body made of the material in question (J/K) n is the amount of substance in the body (mol) R is the gas constant (J⋅K−1⋅mol−1) N is the number of molecules in the body. (dimensionless) kB is the Boltzmann constant (J⋅K−1) Again, SI units shown for example. Read more about the quantities of dimension one at BIPM In the Ideal gas article, dimensionless heat capacity is expressed as . Heat capacity at absolute zero From the definition of entropy the absolute entropy can be calculated by integrating from zero kelvins temperature to the final temperature Tf The heat capacity must be zero at zero temperature in order for