Laws that relate the pressure , volume, and temperature of a gas .
Boyle's law
named for Robert Boyle
states that, at constant temperature, the pressure P of a gas varies inversely with its volume V , or P V = k , where k is a constant. Charles's law
named for J.-A.-C. Charles (1746–1823)
states that, at constant pressure, the volume V of a gas is directly proportional to its absolute (Kelvin) temperature T , or V / T = k . These two laws can be combined to form a single generalization of the behaviour of gases known as an equation of state, P V = n R T , where n is the number of gram-moles of a gas and R is called the universal gas constant. Though this law describes the behaviour of an ideal gas, it closely approximates the behaviour of real gases. See also Joseph Gay-Lussac .