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A corresponding expression for the difference in specific heat capacities (intensive properties) at constant volume and constant pressure is: = where ρ is the density of the substance under the applicable conditions.
In the first, constant-volume case (locked piston), there is no external motion, and thus no mechanical work is done on the atmosphere; C V is used. In the second case, additional work is done as the volume changes, so the amount of heat required to raise the gas temperature (the specific heat capacity) is higher for this constant-pressure case.
Many thermodynamic equations are expressed in terms of partial derivatives. For example, the expression for the heat capacity at constant pressure is: = which is the partial derivative of the enthalpy with respect to temperature while holding pressure constant.
Molar specific heat capacity (isochoric) C nV = / J⋅K⋅ −1 mol −1: ML 2 T −2 Θ −1 N −1: Specific latent heat: L = / J⋅kg −1: L 2 T −2: Ratio of isobaric to isochoric heat capacity, heat capacity ratio, adiabatic index, Laplace coefficient
Heat capacity or thermal capacity is a physical property of matter, defined as the amount of heat to be supplied to an object to produce a unit change in its temperature. [1] The SI unit of heat capacity is joule per kelvin (J/K). Heat capacity is an extensive property.
The specific heat capacity of a substance, especially a gas, may be significantly higher when it is allowed to expand as it is heated (specific heat capacity at constant pressure) than when it is heated in a closed vessel that prevents expansion (specific heat capacity at constant volume).
The Mayer relation states that the specific heat capacity of a gas at constant volume is slightly less than at constant pressure. This relation was built on the reasoning that energy must be supplied to raise the temperature of the gas and for the gas to do work in a volume changing case.
Under these conditions, p 1 V 1 γ = p 2 V 2 γ, where γ is defined as the heat capacity ratio, which is constant for a calorifically perfect gas. The value used for γ is typically 1.4 for diatomic gases like nitrogen (N 2) and oxygen (O 2), (and air, which is 99% diatomic).