How do temperature changes affect the state of a substance?

Temperature changes can cause a substance to change its state, such as from solid to liquid (melting) or liquid to gas (boiling).

When a substance is heated, its particles gain energy. This energy causes the particles to move faster and vibrate more vigorously. In a solid, the particles are closely packed together and vibrate about fixed positions. As the solid is heated and the particles gain more energy, they vibrate so much that they break free from their fixed positions. This is when the solid melts and becomes a liquid. This process is known as melting and the temperature at which it occurs is called the melting point.

Similarly, when a liquid is heated, its particles gain energy and move faster. In a liquid, the particles are not held in fixed positions but can move past each other. As the liquid is heated and the particles gain more energy, they move so fast that they break free from the liquid and become a gas. This process is known as boiling or vaporisation and the temperature at which it occurs is called the boiling point.

Conversely, when a substance is cooled, its particles lose energy. This loss of energy causes the particles to move slower and vibrate less. In a gas, the particles are free to move in any direction. As the gas is cooled and the particles lose energy, they slow down so much that they start to stick together and form a liquid. This process is known as condensation. If cooling continues and the particles lose even more energy, they will vibrate so little that they become fixed in place, forming a solid. This process is known as freezing or solidification.

In summary, temperature changes can cause a substance to change its state by affecting the energy and movement of its particles. The specific temperatures at which these changes occur are unique to each substance and are important characteristics used in chemistry.