Charles’ Law

The Temperature-Volume Relationship

Charles’ Law

French chemist Jacques Charles discovered that the volume of a gas at constant pressure changes with temperature.

As the temperature of the gas increases, so does its volume, and as its temperature decreases, so does its volume.

C h a r l e s ’  L a w

The law says that at constant pressure, the volume of a fixed number of particles of gas is directly proportional to the absolute (Kelvin) temperature, mathematically expressed as:

V = kT

Charles’ Law

V = kT

  V = Volume

  k = Charles’ Law constant   of Proportionality

  T = Temperature in Kelvins

Explanation

Raising the temperature of a gas causes the gas to fill a greater volume as long as pressure remains constant.

Gases expand at a constant rate as temperature increases, and the rate of expansion is similar for all gases.

Example

If the temperature of a given amount of gas is doubled, for example, its volume will also double (as long as pressure remains unchanged).

2V = 2kT

Charles’ Law

Charles’ Law can be modified to a convenient form by solving for k.

k = V / T

Charles’ Law

In a sample with volume V1 & temperature T1, changing either volume or temperature converts these variables to V2 and T2.

V1 / T1 = k = V2 / T2

Therefore:

V1 T2 = V2 T1

Demonstration of Charles’ Law

Relationship of Boyle’s Law and Charles’ Law

Practical Applications

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