The process of changing a substance from one physical state to another at a definite temperature is known as a change of state.
At room temperature, for example, water molecules are in a liquid state. When water is heated to \(100\) degrees Celsius, it turns into steam, a gaseous state of matter. When the temperature of the steam is reduced, it reverts to water. If we lower the temperature to \(0°C\), it turns into ice, which is a solid-state of water. When ice melts, it reverts to water. As a result, when the temperature changes, water changes its state. There are various such processes in the matter's change of state.
Change of state of matter
Melting or fusion is the process of converting a solid into a liquid by absorbing heat. The melting point is the temperature at which a solid transforms into a liquid. Freezing is the polar opposite of melting. Freezing is the process of converting a liquid to a solid by releasing heat. The freezing point is the temperature at which a liquid transforms into a solid. Melting and boiling occur at \(0°C\) in the case of water.
The temperature at which a liquid changes its state to gas is called the boiling point. The process in which vapour is converted to a liquid by releasing heat is called condensation. Condensation point is the temperature at which a gas changes from a gas to a liquid. Water has a boiling point of \(100°C\) and a condensation point of \(100°C\).
The process in which a liquid is converted to vapour by absorbing heat is called boiling or vaporization.
Dry ice, iodine, frozen carbon dioxide, and naphthalene balls are examples of solids that change from solid to the gaseous state without becoming liquid.
Sublimation is the process of transforming a solid into a gaseous state.
Various stages of heat-induced state conversion with corresponding temperature changes.