When a solid is heated then there is increase in temperature which causes breakage in between strong intermolecular bonds of the atoms. As a result, the atoms move at a distance and start to collide.
Thus, there will be increase in the kinetic energy and there will be change in the state of matter.
For example, when ice is kept at room temperature then it starts to melt because of the surrounding heat. As a result, it changes into water.
H2O(*) + heat → H2O(l)
On further increasing the temperature, the liquid state will convert into gaseous state.
Similarly, when we increase pressure on a liquid substance or matter then the molecules start to come closer to each other. As a result, the liquid state will change into solid.
H2O(l) + pressure → H2O(*)
Also, when pressure is increased on a gas it will start to convert into liquid state.
