IDEAL GASES Ideal gas laws and the equation of state.
THE GAS LAWS
There are three gas laws, deduced experimentally and mostly named after the discoverer.
Boyle's law.
Boyle's law states that for a certain mass of gas, at a constant temperature the product of volume and temperature is a
constant.
p V = k
Charle's law.
Charle's law states that for a certain mass of gas, at a constant pressure the volume is directly proportional to temperature.
V / T = k
The pressure law.
The Pressure law states that for a certain mass of gas, at a constant volume the pressure is directly proportional to temperature.
p / T = k
THE EQUATION OF STATE
There are no gases that obey the above laws exactly, however they do provide a good approximation when the gas is far above its boling point and
at a reasonably low pressure. A theoretical gas that obeys the laws exactly is know as an ideal gas. Combining the above laws gives what is
known as the equation of state for an ideal gas. This is
p V = n R T
where p is the pressure, V is the volume, n is the amount in mols of the gas, T is the temperature in Kelvins and
R is the universal molar gas constant ( = 8.3 J K-1 mol-1).
Notes:
- Temperature's are measured in Kelvins, equal in value to centigrade but shifted so that 00C is 273 K.
- Zero Kelvin, is defined by the equation p V = n R T. This can be duduced graphically by drawing a graph of
p V against T, a straight line, and finding the value of T when p V = 0.
Rob Coles 10 April 1996 17:07:46