Ideal gas law
The ideal gas law is useful for calculating temperatures, volumes, pressures or number of moles for many gases over a wide range of temperatures and pressures. However, the law fails at low temperatures or high pressures. The ideal gas law is the combination of Boyle's law, Charles's law and Avogadro's law and is expresses as:
IDEAL GAS LAW: PV = nRT,
where P = pressure, V = volume, n = number of moles, R = 0.082057 (L x atm)/(K x mol), the constant of proportionality relating the molar volume of a gas to T/P (the "molar gas constant"), and T = the absolute temperature, in degrees Kelvin.
Boyle's law: V = constant/P (at fixed temperature and amount of gas)
Charles's law: V = contant x T (at fixed pressure and amount of gas)
Boyle's + Charles's PV/T = constant (at fixed amount of gas)
Avogadro's law: V = nV, (at fixed temperature and pressure, where V is the same for all gases
The gas laws started, in the 1660's, with Robert Boyle's law, stating "the volume of a sample of gas at a given temperature varies inversely with the applied pressure, or V = constant/P (at fixed temperature and amount of gas). Then Jacques Alexandre Charles' experiments with hot-air balloons, and additional contributions by John Dalton (1801) and Joseph Louis Gay-Lussac (1802) showed that a sample of gas, at a fixed pressure, increases in volume linearly with the temperature, or V/T = a constant. This is known as Charles's law. Extrapolations of volume/temperature data for many gases, to a volume of zero, all cross at about -273 degrees C, which is absolute zero. Of course, the gases would liquify before reaching this temperature and so the law does not really apply in this temperature region. In 1811 Amedeo Avogadro re-interpreted Gay-Lussac's law of combining volumes (1808) to state Avogadro's law , Equal volumes of any two gases at the same temperature and pressure contain the same number of molecules. The molar volume of gas, at standard temperature ( 0 Celcius) and pressure (1 atm) is 22.4 L.