Charles's Law

The law that, at constant pressure, the volume of a sample of a gas is directly proportional to the Kelvin temperature is called Charles's law.

Charles's law states that at constant pressure, the volume of a sample of a gas is directly proportional to the Kelvin or absolute temperature:

V = (a constant)(T)

or:

V
T
 = a constant

Increasing the temperature of a sample of a gas at constant pressure increases the volume of the gas.

Charles's law makes possible calculation of any one of the four variables, V1, V2, T1, or T2, if the values of the other three are known. For example, if (V1/T1) = a constant and (V2/T2) = the same constant, then:

V1
T1
 = 
V2
T2

rearranging:

T1
V2
V1
 = T2

and:

V1
T2
T1
 = V2

If the temperature of a sample of gas is changed while the pressure is kept constant, the old volume, V1 can be converted to the new volume V2 by multiplying the old volume by (T2/T1). Reason from the fact that when a sample of a gas is heated at constant pressure, volume increases.