When studying the properties of gases, you need to know the relationships between the variables of volume (V), pressure (P), Kelvin temperature (T), and the amount in moles (n) so that you can calculate missing information (P, V, T, or n) and solve reaction stoichiometry problems. Although the pairs of variables have individual relationships, the two most important and useful gas laws are the combined gas law and the ideal gas law:

Combined gas law (P1V1)/T1 = (P2V2)/T2 (T must be in Kelvin)
Ideal gas law PV = nRT (R = 0.0821 L atm/K.mol)