The modern approach to thermodynamics is based on the concept of a system whose equilibrium state is determined by its properties. For a system comprising a pure substance, two properties only may be sufficient to determine completely the equilibrium state. Pressure, volume and temperature are the most common, and most easily measured, properties and, for an ideal gas, these are connected by a simple equation of state, which may be expressed in the following forms
pv = RT
pV = mRT = nR 0 T
pVM = R 0 T
A perfect gas has the additional characteristic of constant specific heats.
n = number of moles of gas
V M = molar volume = 22.413 6 m3 /kmol
R0 = universal gas constant = 8.314 3 kJ/kmol K.
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© E. M. Goodger 1984