Substance A has a normal fusion point of ‑10.0 oC, an enthalpy of fusion = 150.0 J g^-1; specific heats for the solid and the liquid are 3.00 and 6.20 J g^-1 oC^-1, respectively. How much heat, in J, is required to change 150 grams of A from a solid at –40.0 oC to a liquid at +70.0 oC?

Answer 1

There are two formula to use and you can progress from the solid, liquid, gas.

When you change the phase, you go with q = mass x heat fusion (at the melting point) or q = mass x heat vap at the boiling point.

When the phase is not changing, you go with q = mass x specific heat x (Tfinal-Tinitial).
This applies in the solid phase, the liquid phase, and the gaseous phase.
Then total q = sum of the individual qs. Post your work if you get stuck.