<Dd> Z = P V m R T . (\ displaystyle Z = (\ frac (PV_ (\ mathrm (m))) (RT)).) </Dd> <Dl> <Dd> ln ⁡ φ = ∫ 0 P (Z − 1 P) d P . (\ displaystyle \ ln \ varphi = \ int _ (0) ^ (P) \ left ((\ frac (Z - 1) (P)) \ right) dP .) </Dd> </Dl> <Dd> ln ⁡ φ = ∫ 0 P (Z − 1 P) d P . (\ displaystyle \ ln \ varphi = \ int _ (0) ^ (P) \ left ((\ frac (Z - 1) (P)) \ right) dP .) </Dd> <P> This is useful because of the theorem of corresponding states: If the pressure and temperature at the critical point of the gas are P and T, we can define reduced properties P = P / P and T = T / T. Then, to a good approximation, most gases have the same value of Z for the same reduced temperature and pressure . However, in geochemical applications, this principle ceases to be accurate at pressures where metamorphism occurs . </P>

When a liquid is transformed into its vapor at constant temperature