Specific heat capacity

Description

Specific heat capacity is a material property that relates changes in a material’s temperature to the energy transferred to or from the material by heating (either heating the material or by allowing it to heat its surroundings).

When raising the temperature of a material by transferring energy into the material by heating, the specific heat capacity of the material is defined as the energy transferred per unit mass per unit temperature rise.

Specific heat capacity is usually represented by the symbol c.

If the temperature of a mass m of the material changes by ΔT, the associated energy Q transferred into the material by heating is

Q = mcΔT

Discussion

In general, the specific heat capacity is a measure of how much energy it takes to change the temperature of a system. But in the definition, it is important to realise that the energy input must be by heating. If work is done on the system, in general, its temperature will increase but it is not correct to try to calculate the temperature rise using the heat capacity and the amount of work done on it. Another factor that can be important is the constraint under which the system is held. The specific heat capacity of a system held at constant volume is different from that of one held at constant pressure as the latter does work on its surroundings as it expands. Such differences can usually be ignored for solids but they are very important when dealing with gases.

SI unit

J kg^-1 K^-1

Expressed in SI base units

m² s^-2 K^-1

Other commonly used unit(s)

J kg^-1 °C^-1, J kg^-1 °F^-1

Mathematical expressions

• If the temperature of a mass m of a material changes by ΔT, the associated energy transferred into the material by heating is
  Q = mcΔT

Related entries

• Energy of a system
• Internal energy

In context

The specific heat capacity of water at room temperature is 4181 J kg^-1 K^-1, that of copper is 390 J kg^-1 K^-1 and that of a typical oil is 2000 J kg^-1 K^-1. Ceramic materials such as concrete or brick have specific heat capacities around 850 J kg^-1 K^-1.

The relatively high specific heat capacity of water means that it is very useful in central heating systems, because it is able to transfer a great deal of energy by heating while its temperature changes by a relatively small amount. In storage heaters, where the relevant substance remains in the heater, solids such as clay bricks or ceramic materials are preferred, as they do not leak or corrode their containers, although their lower specific heat capacity means that they have to be raised to a very high temperature to supply useful heating over several hours.