Charles's law is a gas law that states gases expand when heated. The law is also known as the law of volumes. The law takes its name from French scientist and inventor Jacques Charles, who formulated it in the 1780s.

### Charles's Law Definition

Charles's Law is an ideal gas law where at constant pressure, the volume of an ideal gas is directly proportional to its absolute temperature. The simplest statement of the law is:

V/T = k

where V is volume, T is absolute temperature, and k is a constant

V_{i}/T_{i} = V_{f}/T_{f}

where

V_{i} = initial pressure

T_{i} = initial temperature

V_{f} = final pressure

T_{f} = final temperature

### Charles's Law and Absolute Zero

If the law is taken to its natural conclusion, it appears the volume of a gas approaches zero and its temperature nears absolute zero. Gay-Lussac explained this could only be true if the gas continued to behave as an ideal gas, which it was not. Like other ideal gas laws, Charles's law works best when applied to gases under normal conditions.