Final answer:
The energy required for a substance to change from the liquid phase to the vapour phase is called the c) heat of vaporization, which is the correct answer to the question.
Step-by-step explanation:
To understand the energy needed for a phase change to a gas, we focus on the concept of the heat of vaporization. This is the energy per unit mass required to change a substance from the liquid phase to the vapour phase. In other words, the heat of vaporization is the amount of energy needed to turn a liquid into a gas without changing its temperature. It involves overcoming the molecular attractions in the liquid to allow the molecules to separate and form a vapour. Considering the provided options, the correct answer is c) Heat of vaporization, which directly relates to the energy required for the liquid-to-gas phase change. This concept is key in the study of thermodynamics, a core topic in chemistry dealing with heat and energy transformations.