We have already discussed temperature, pressure and density. A few other examples are heat capacity, viscosity, thermal conductivity, and electrical conductivity. Of particular importance is the question of how many of these properties can be regarded as independent variables. This result will have some importance in the following pages, where we will discuss the relationship between pressure, specific volume and temperature for a pure substance. Before moving on, let us summarize the important points about properties.
Extensive properties depend upon the size of the system.
Intensive properties apply at a point. For a single phase of a pure substance, specifying values of any two variables fixes the remaining ones.