# Explanation of Changes in Temperature and State of Substance

## Explanation of Changes in Temperature and State of Substance

• Temperature is a measure of the average kinetic energy of the particles in a substance. This means it is the average energy of the movement (vibrations and random motion) of the atoms or molecules in the material.

• When heat is added to a substance, it increases the kinetic energy of the particles causing them to move more quickly and randomly. This increase in kinetic energy is measured as an increase in temperature.

• As more heat is added, causing the temperature to rise, the kinetic energy of the particles also rises until a certain point - the substance’s melting point or boiling point.

• The melting point is the temperature at which a solid turns into a liquid. At this temperature, the particles have enough energy to overcome the forces holding them together in the solid structure.

• Energy absorbed during melting or evaporation is used to break the bonds between molecules rather than to increase their kinetic energy or the temperature. This is called latent heat.

• Latent heat is the heat energy required to change the state of a substance without changing its temperature. It includes latent heat of fusion (for melting) and latent heat of vaporisation (for boiling).

• The boiling point is the temperature at which a liquid turns into a gas. At this temperature, the particles have enough energy to overcome the intermolecular forces keeping them in the liquid state and become a gas.

• Upon reaching the boiling point, the temperature no longer increases even with the addition of more heat. Instead, the heat is used to break the bonds between the molecules, converting the liquid to gas.

• A process called sublimation can also occur, whereby a substance transitions from a solid directly to a gas without passing through the liquid phase. This happens when the particles in the solid phase have sufficient energy to bypass the liquid stage.

• When heat is removed from a substance, its particles begin to lose kinetic energy and slow down, leading to a drop in temperature. If enough heat is removed, the substance may change from a gas to a liquid (condensation), or a liquid to a solid (freezing).

• Each substance has unique boiling and melting points due to the variance in intermolecular forces, which depend on the molecular composition and structure of the substance.

• In gases, the kinetic energy of molecules is the greatest because the intermolecular forces are weakest. In solids, kinetic energy is the lowest because the particles are closely packed and can only vibrate in place due to strong intermolecular forces.

• In summary, changes in temperature and state of a substance can be explained through the changes in the kinetic energy of its particles and the way this energy is used to overcome intermolecular forces.