Basic science

Heat capacity is the amount of heat energy required to raise a given object by one kelvin, and has the unit J·K⁻¹.

Specific heat capacity is the amount of heat energy required to raise one kilogram of a substance by one kelvin, without causing a change in state. It is measured in J·kg⁻¹·K⁻¹.

Solids and liquids tend to have higher specific heat capacities than gases. For example, the specific heat capacity for water is approximately four times higher than for air (4160 versus 998 J·kg⁻¹·K⁻¹).

All molecular and atomic particles exert attractive and repulsive forces on each other known as intermolecular forces of attraction. In a solid these particles oscillate about a fixed position, which maintains a given shape and volume. The addition of heat increases the kinetic energy of the molecules, until eventually the particles gain sufficient energy to overcome the intermolecular forces of attraction. When this happens the solid loses its fixed structure to become a liquid. This is known as the melting point.

A liquid is a nearly incompressible fluid that conforms to the shape of its container and has a constant volume. At its boiling point the molecules have sufficient energy to break free of the intermolecular forces of attraction and enter the gaseous phase.

When heat is applied to matter, temperature increases until the melting or boiling point is reached. At these points the addition of further heat energy is used to change the state of matter from solid to liquid and from liquid to gas. This does not cause a change in temperature. The energy required at these points is referred to as latent heat of fusion and latent heat of vaporisation, respectively.

Specific latent heat is the heat required to convert one kilogram of a substance from one phase to another at a given temperature. As temperature increases, the amount of additional energy required to overcome the intermolecular forces of attraction falls until the critical temperature of a substance is reached. At this point the specific latent heat is zero, as no further energy is required to complete the change in state of the substance.