Matter & Energy


Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.

Charles’s Law of Gas

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. French chemist Joseph Guy-Lussac refined Charles’s theory, and the law is also known as Guy-Lussac’s law.

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. Charles's law (also called Gay-Lussac’s law) describes the relationship between volume and temperature of an enclosed gas. 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 = k T

where T is temperature on the Kelvin scale (see Temperature: Temperature Scales). If the temperature of a given amount of gas is doubled, for example, its volume will also double (as long as pressure remains unchanged).