A property that depends upon the quantity of the substance or substances present in the system is called the capacity or extensive property.

The common examples of these properties are mass, volume, energy, heat capacity, etc. The extensive properties are additive, i.e., the total value of an extensive property is equal to the sum of the values for the separate parts into which the system may be divided for the sake of convenience.

A property which depends only upon the nature of the substance and not on the amount(s) of the substance(s) present in the system is known as intensity or intensive property. The common examples of these properties are temperature, pressure, concentration, refractive index, viscosity, density, surface tension, specific heat, etc. The quotient obtained by dividing any extensive variable by another extensive variable gives an intensive variable. For example, concentration (moles/liter), density (mass/volume), mole fraction (n/N), specific heat(heat capacity per unit mass).

The extensive properties of a single (pure) substance depends upon the number of moles (n) of the substance and also on any two of the three variables P, V and T(called independent variable). However, if n is kept constant, the extensive properties of the system will depend only on the two independent variables.

The extensive properties of a system consisting of a solution of two or more substances will depend on the number of moles (n) etc., of the constituents A, B, C, etc., and also on the two independent variables. The intensive properties in such cases will depend upon the concentration of the various species, besides the two independent variables.

The ideal gas equation, PV = nRT has two extensive variables (n and V) and two intensive variables (P and T). However, if the two extensive variables n and V of the ideal gas equation are fused into each other, the resulting expression has three intensive variables c, P and T.