Why do gases expand when heated?

Gases expand when heated because the increased temperature causes the gas particles to move faster and spread out more.

In more detail, the behaviour of gases can be explained using the kinetic theory of gases. This theory states that gases are made up of a large number of tiny particles that are in constant, random motion. The particles are considered to be perfectly elastic, meaning they do not lose energy when they collide with each other or the walls of their container.

When a gas is heated, the energy from the heat is transferred to the gas particles. This causes the particles to move faster, increasing their kinetic energy. As the particles move faster, they collide with each other and the walls of their container more frequently and with greater force. This increased activity causes the gas to expand.

The expansion of gases when heated is also related to the concept of pressure. Pressure is defined as the force exerted by a gas per unit area on the walls of its container. When the gas particles move faster and collide more frequently, they exert a greater force on the walls of their container, increasing the pressure. If the container is flexible, like a balloon, it will expand as the pressure increases.

This behaviour of gases is described by Charles's Law, which states that the volume of a gas is directly proportional to its absolute temperature, provided the pressure and the amount of gas remain constant. This means that if the temperature of a gas is increased, its volume will also increase, assuming the pressure and amount of gas are kept constant. Conversely, if the temperature of a gas is decreased, its volume will decrease. This law helps to explain why gases expand when they are heated.