Define enthalpy of sublimation?

The enthalpy of sublimation is the amount of heat energy required to change a substance from a solid directly to a gas, without passing through the liquid phase. It is the sum of the enthalpy of fusion (melting) and the enthalpy of vaporization (boiling) of the substance.

The enthalpy of sublimation is the amount of energy required to convert one mole of a substance from the solid phase directly into the gas phase. It is a thermodynamic property that measures the heat absorbed by a substance during sublimation, which is the process of a solid changing directly into a gas without going through the liquid phase.