heat capacity

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The quantity of heat required to raise a unit mass of homogeneous material one unit in temperature along a specified path, provided that during the process no phase or chemical changes occur, is known as the heat capacity of the material. Moreover, the path is so restricted that the only work effects are those necessarily done on the surroundings to cause the change to conform to the specified path. The path is usually at either constant pressure or constant volume.

In accordance with the first law of thermodynamics, heat capacity at constant pressure C_p is equal to the rate of change of enthalpy with temperature at constant pressure (∂H/∂T)_p. Heat capacity at constant volume C_v is the rate of change of internal energy with temperature at constant volume (∂U/∂T)_v. Moreover, for any material, the first law yields the relation shown in the equation below. See also Enthalpy; Internal energy.

In physics, the capability of a substance to absorb energy in the form of heat for a given increase in temperature. Materials with high heat capacities, such as water, require greater amounts of heat to increase their temperatures than do substances with low heat capacities, such as metals. (See entropy.)