How does a gas change when it is heated at constant pressure?

When a gas is heated at a constant pressure, it undergoes thermal expansion, meaning its volume increases. This relationship is described by Charles’s law, which states that the volume occupied by a fixed amount of gas is directly proportional to its absolute temperature when the pressure remains constant.1

For example, at room temperature, an increase of 1°C causes the volume of a gas to increase by approximately 0.3 percent. This behavior is a fundamental aspect of the ideal gas law, which accurately describes the properties of dilute gases under most conditions.12