Heat capacity

Heat capacity or thermal capacity is a physical property of matter, defined as the amount of heat to be supplied to a given mass of a material to produce a unit change in its temperature. Heat capacity or thermal capacity is a physical property of matter, defined as the amount of heat to be supplied to a given mass of a material to produce a unit change in its temperature. The SI unit of heat capacity is joule per kelvin (J/K). Heat capacity is an extensive property. The corresponding intensive property is the specific heat capacity. Dividing the heat capacity by the amount of substance in moles yields its molar heat capacity. The volumetric heat capacity measures the heat capacity per volume. Heat capacity is often said as thermal mass in architecture and civil engineering to refer to the heat capacity of a building . The heat capacity of an object, denoted by C {displaystyle C} , is the limit where Δ Q {displaystyle Delta Q} is the amount of heat that must be added to the object (of mass M) in order to raise its temperature by Δ T {displaystyle Delta T} . The value of this parameter usually varies considerably depending on the starting temperature T {displaystyle T} of the object and the pressure P {displaystyle P} applied to it. Therefore, it should be considered a function C ( P , T ) {displaystyle C(P,T)} of those two variables. However, the variation can be ignored in contexts when working with objects in narrow ranges of temperature and pressure. For example, the heat capacity of a block of iron weighing one pound is about 204 J/K when measured from a starting temperature T=25 °C and P=1 atm of pressure. That approximate value is quite adequate for all temperatures between, say, 15 °C and 35 °C, and surrounding pressures from 0 to 10 atmospheres, because the exact value varies very little in those ranges. One can trust that the same heat input of 204 J will raise the temperature of the block from 15 °C to 16 °C, or from 34 °C to 35 °C, with negligible error. At constant pressure, heat supplied to the system would contribute to both the work done and the change in internal energy, according to the first law of thermodynamics. The heat capacity would be called C P {displaystyle C_{mathrm {P} }} . A system undergoing a process at constant volume would imply that no work would be done, so the heat supplied would contribute only to the change in internal energy. The heat capacity obtained this way is denoted C V {displaystyle C_{mathrm {V} }} . The value of C V {displaystyle C_{mathrm {V} }} is always less than the value of C P {displaystyle C_{mathrm {P} }} .