• → 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)
    1. Heat to melting point: q = mcΔT
    2. Melting: q = (moles)
    3. Add up values

  • Value of c will be different in each phase

  • Remember: for exothermic, final answer (q) will be negative