State of a System
In an ideal gas, the pressure p, volume V, and temperature T are related by the ideal gas law pV = nRT, where n is the number of moles and R = 8.31 J/K/mol.
Using this equation, if we know n, p and V, we can calculate T. In a real gas, the relation between p, V and T is more complicated. It is still true that for a give p and V, we always get the same T. p and V tell us something about the gas. We call this the state of the gas. So T is determined by the state of the system.
Fixing the pressure and volume of a gas fixes the state of the gas. By "state," we mean the n, p, V and T. That is, if I have the same number of moles of nitrogen in two bottles, the was they can be different are by having different p, V or T. There are no other ways that they can be different, except for the random motion of the molecules.
p and V determines T, and T determines the internal energy. So the state of a gas
determines the internal energy, which is the total kinetic and potential energies
of the molecules. This gives us a convenient way to completely describe a gas.
If we specify n, p and V, we fix the T and the internal energy as well.
Copyright 2010 by Kai Hock. All rights reserved.
Last updated: 19 October 2010.