Which law states that the volume of a gas is directly proportional to its temperature?

The General Gas Law supports the idea that the volume of a gas is directly proportional to its temperature when pressure is held constant. This principle is encapsulated in Charles's Law, which is a subset of the General Gas Law. According to Charles's Law, if you take a fixed amount of gas and maintain a constant pressure, any increase in temperature will result in an increase in volume, and conversely, a decrease in temperature will lead to a reduction in volume. This relationship is critical in power engineering, as it affects various processes such as thermodynamics in engines and heating systems.

The other laws listed do not pertain specifically to the relationship between gas volume and temperature. The Law of Conservation of Matter describes how matter cannot be created or destroyed in a chemical reaction, the Law of Combining Masses relates to the accurate measurement of mass in chemical reactions, and the Law of Conservation of Energy deals with the principle that energy cannot be created or destroyed, only transformed. Consequently, the General Gas Law is the relevant law when discussing the volumetric response of gases to temperature changes.