You're right, the formula Q = mHf is used to calculate the heat absorbed or released during a phase change (melting or freezing). Here's what the variables represent:

* Q: Represents the heat energy absorbed or released during the phase change, usually measured in joules (J) or calories (cal).

* m: Represents the mass of the material undergoing the phase change, typically measured in grams (g) or kilograms (kg).

* Hf: Represents the enthalpy of fusion, also known as the latent heat of fusion. This is a specific value for a given substance that represents the amount of heat energy required to melt one unit of mass of the substance at its melting point. It's measured in joules per gram (J/g) or calories per gram (cal/g).

Let me know if you'd like to work through an example problem!