How is thermochemistry used for phase changes?
Thermochemistry is used to calculate the amount of energy required to change from state to state.
For example, if you need to change from solid water to liquid, there is a constant known as heat of sublimation (specific heat), which has been experimentally determined. However, there is a constant for all liquids and that can be derived with simple algebra. Without making things complicated, here is a table to help guide you: