The calculation object of constant volume specific heat capacity is gas. Because when the pressure is constant and the temperature rises, the gas will inevitably expand and do work. In addition to the heat required to raise the temperature, a part of heat is needed to compensate the work done by the gas. Therefore, the specific heat capacity of gas at constant pressure is greater than that at constant volume.
The definitions of constant pressure specific heat capacity and constant volume specific heat capacity are applicable to all working fluids.
Because the gas expands when heated under constant pressure, the absorbed heat can not only increase the thermodynamic energy, but also overcome the external force to do work, so the specific heat capacity under constant pressure is greater than that under constant volume, and the difference is the external work when the gas is heated under constant pressure.
The specific heat capacity of gas at constant pressure is greater than that at constant volume. Because the physical states of solids and liquids have not changed, the heat provided by the outside world is used to change the temperature, and its volume changes very little, so the difference between the specific heat capacity at constant pressure and that of solids and liquids will not be too great. So there is no need to distinguish.
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