Final answer:
The effect of changing volume on the melting/boiling point of a substance depends on external conditions like pressure. It raises melting and boiling points under high pressure and lowers them under low pressure. The energy change during a phase change is proportional to the mass of the substance.
Step-by-step explanation:
How changing volume affects the melting/boiling point of a substance depends largely on the external conditions, particularly pressure. High pressure generally raises melting points and boiling points because it favors the denser phase of matter, while low pressure tends to lower them. For instance, the boiling point of water is 100 °C at 1.00 atm, but this changes with pressure. Moreover, when heat adds energy to a system, it can lead to an increase in both pressure and volume, further demonstrating how changing volume can affect these state changes. Therefore, the correct answer is d) It depends on the substance.
During a phase change such as melting or boiling, the substance absorbs or releases energy without changing temperature. This energy, known as latent heat, is directly proportional to the mass of the substance involved in the phase change. Thus, a large mass requires a correspondingly large amount of energy to change its phase.