Final answer:
The enthalpy of vaporization for a substance can be represented by the horizontal line on a heating curve where the temperature remains constant.
Step-by-step explanation:
The enthalpy of vaporization for a substance can be represented by the horizontal line on a heating curve where the temperature remains constant. On a heating curve, the enthalpy of vaporization is the heat added during the phase change from liquid to gas. This line will be longer compared to the line for the enthalpy of fusion because the enthalpy of vaporization is several times greater.