Energy transfer in changes of state

Particle Theory

For the particles in a solid to change into a liquid, the bonds between the particles must be loosened enough to allow them to flow around each other, giving them the properties of a liquid. For this to happen, energy is required. This energy comes from the surroundings and into the particles, giving them the required energy to stretch the bonds. All reactions that involve energy coming in from the surroundings are endothermic by definition, so we can see that melting is endothermic.

Exothermic vs Endothermic

Endothermic is a reaction that takes in energy from its surroundings causing it to feel cool to the touch. Exothermic reactions release energy to the surroundings an example of this would be a water vapour condensing to water.