- → endothermic (attractive forces are being broken; final answer [ΔH or q] = +); ← exothermic (attractive forces are forming; final answer [ΔH or q] = -)
○ Heat of fusion 
will be positive for melting and negative for freezing; heat of vaporization will be positive for vaporization and negative for condensation
- Can’t use q = mcΔT during phase changes bcuz temp remains constant
○ No change in KE, only change in PE
○ During HoV, all the intermolecular forces/attraction are breaking but during HoF are only breaking/separating some
- Energy required for phase changes (ex: required to melt a substance)
-
- Heat to melting point: q = mcΔT
- Melting: q = (moles)
- Add up values
- Value of c will be different in each phase
- Remember: for exothermic, final answer (q) will be negative