DESCRIPTION OF IDEAL GAS EQUATION
Avogadro's law tells us that at constant P and T, the volume of a gas is directly proportional to the amount of gas. Boyle's law says that volume is inversely proportional to pressure, and Charles' indicates that volume is directly proportional totemperature. These three laws may all be applied at once if we write
or, introducing a constant of proportionality R,
or we can also write PV = nRT
Equation (2) applies to all gases at low pressures and high temperatures and is a very good approximation under nearly all conditions.