Define and explain enthalpy of phase transformation.

Explanation

The conversation of solid to liquid is called melting or fusion and the process of conversion of liquid into gas is called vapourisation. These processes are collectively called phase transformation or phase changes.
The enthalpy change accompanying the conversation of 1 mole of a solid substance into the liquid state at its melting point is called enthalpy of fusion.
The enthalpy change accompanying the conversation of one mole of liquid into its vapours at the boiling called enthalpy of vapourisation.