The enthalpy of fusion is the amount of energy required to change a substance from a solid state to a liquid state at a constant pressure and temperature.
The enthalpy of fusion is calculated by dividing the amount of energy required to melt a substance by the mass of the substance. It is typically measured in units of joules per gram (J/g).
The enthalpy of vaporization is the amount of energy required to change a substance from a liquid state to a gaseous state at a constant pressure and temperature.
The enthalpy of vaporization is typically higher than the enthalpy of fusion, as it takes more energy to overcome the attractive forces between molecules in a liquid state compared to those in a solid state.
The enthalpy of fusion, vaporization, and sublimation can be measured for most substances. However, certain substances may not have a distinct melting or boiling point, making it difficult to accurately measure these values. Additionally, some substances may undergo a phase change directly from solid to gas, without passing through a liquid state.