2. Fluid properties

2.1 Pure-body equations of state

Consider a single pure body, constituting a single fluid phase. The phase rule (20) shows that v = 2. This indicates that there are two variables that can be given independently to characterize the state of the fluid, e.g. temperature and pressure. All other variables are functions of the two initially chosen. If we consider, for example, the volume occupied by a given quantity of substance, we have a relationship f (P, V, T ) = 0, which is the equation of state. As such, this equation is independent of macroscopic thermodynamics.