The heat of vaporization is the amount of energy that is required to convert a substance from liquid to gaseous state without changing its temperature. A substance with a high heat of evaporation takes longer to transform between the two states.
The heat of evaporation is mainly dependent on the strength of intermolecular bonds. Substances with strong intermolecular bonds are more likely to have high heat of evaporation than those with weaker ones. When a substance reaches its boiling point, its temperature stagnates until all the substance is converted to a gas. All the heat energy exerted on the substance is used for breaking the intermolecular bonds. This is where the relationship between the heat of evaporation and intermolecular bond strength arises.