What factor does Charles' Law state is directly proportional to the volume of a gas?

Charles' Law states that the volume of a gas is directly proportional to its absolute temperature when the pressure is kept constant. This means that if the temperature of the gas increases, the volume will also increase, provided the pressure does not change. The relationship can be expressed mathematically as V ∝ T, where V is volume and T is absolute temperature measured in Kelvin.

This principle is crucial in understanding how gases behave under different thermal conditions. For instance, when you heat a balloon filled with air, the air inside expands, increasing the volume of the balloon. This is a practical application of Charles' Law, demonstrating the direct relationship between temperature and volume in gas behavior.