Heat Capacity

Two versions of the quantity are in use and they are not interchangeable. The heat capacity at constant volume counts only the energy that raises internal energy, while the value at constant pressure also covers the work done as the substance expands; for an ideal gas the two differ by the gas constant. Dividing by mass gives specific heat capacity and dividing by amount of substance gives molar heat capacity. Water is the reference case for how large the property can be, at about 4.18 joules per gram per kelvin, a value that follows from extensive hydrogen bonding and that moderates both climate and biological temperature. In solids the molar value approaches roughly 25 joules per mole per kelvin at ordinary temperature, the empirical regularity known as the Dulong-Petit law.