Introduction:
When a substance changes from one state to another, it undergoes a physical change, and its properties change as well. To understand what happens inside the matter during the change of state, we need to look at the behavior of the molecules that make up the substance.

Solid to Liquid:
When a solid substance is heated, the energy is absorbed by the molecules, and they start vibrating more vigorously. As the temperature rises, the molecules start to move apart and overcome the forces that hold them together. Eventually, the molecules have enough energy to break the bonds between them, and the solid substance melts into a liquid.

Liquid to Gas:
When a liquid is heated, the molecules gain enough energy to overcome the attractive forces that hold them together. As a result, they start to move apart and move more freely. The liquid becomes less dense and turns into a gas.

Solid to Gas:
When a solid is heated, its molecules start to vibrate more vigorously. As the temperature rises, the molecules gain enough energy to overcome the attractive forces that hold them together. They start to move apart and move more freely. Eventually, the molecules have enough energy to break the bonds between them, and the solid turns into a gas.

Gas to Liquid:
When a gas is cooled, its molecules lose energy, and they move more slowly. As a result, they start to come closer together and overcome the repulsive forces that keep them apart. Eventually, the molecules are close enough to form bonds with each other, and the gas turns into a liquid.

Liquid to Solid:
When a liquid is cooled, its molecules lose energy, and they move more slowly. As a result, they start to come closer together and overcome the repulsive forces that keep them apart. Eventually, the molecules are close enough to form bonds with each other, and the liquid turns into a solid.

Conclusion:
In conclusion, the change of state in matter occurs due to the gain or loss of energy. The behavior of molecules plays a significant role in determining the state of matter. The understanding of these changes is crucial in various fields, including science and engineering.

During change of state if solid is heated to get converted into liquid , the heat is used up to break the intermolecular force of attraction of particle of solid.It is also in coversion of liquid to gas.