 The gas laws define the behavior of an ideal gas, typically through mathematical equations.  The laws examine the relationships between temperature, pressure, volume, and amount of gas.

Boyle's Law:  Pressure-Volume

Boyle discovered that while temperature and quantity were held constant during two observations of different conditions of one gas, pressure and volume were inversely proportional.  This means that when pressure increases, volume decreases, and vice versa.  The equation that explains this concept is as follows:
P1 V1 = P2 V2
Given  three of the variables from the equation, you can calculate the fourth variable by rearranging the equation.  For example,  suppose that from one observation of a gas sample you know the pressure and volume.  From a second observation you know only the volume.  To calculate the second pressure value, multiply the first pressure and volume values, then divide by the second volume value.

Charles' Law:  Volume-Temperature

Charles discovered that while quantity and pressure are held constant, volume varies directly with the temperature.  The equation that explains this is as follows:
V1 = V2
T1     T2

Gay-Lussac:  Pressure-Temperature

Gay-Lussac discovered that while volume and quantity are held constant, pressure and temperature are directly proportional.  This law is expressed as follows:
P1 = P2
T1    T2

The Combined Gas Law

The combined gas law is derived from the three previously mentioned laws.  It relates pressure, volume, and temperature of a gas when quantity is held constant.  The law is expressed by the following equation:
P1 V1 = T1
P2 V2    T2

Visit the next page on this site for a more complete explanation of the combined gas law (or click here:
The Combined Gas Law:  An In-Depth Look )