The phase changes that involve transfer of heat from the surroundings to the system are the endothermic ones:

  • Melting (solid → liquid)
  • Vaporization/boiling/evaporation (liquid → gas)
  • Sublimation (solid → gas)

Key idea

When heat flows from surroundings into a substance, the process is endothermic and the system absorbs energy without necessarily changing temperature during the phase change.

  • In melting , a solid absorbs heat to loosen particle bonds and become a liquid.
  • In vaporization , a liquid absorbs heat so particles can escape into the gas phase.
  • In sublimation , a solid absorbs enough energy to jump directly to the gas phase.

How to spot the right answer

If your options are things like:

  • Freezing (liquid → solid)
  • Condensation (gas → liquid)
  • Deposition (gas → solid)
  • Melting / Vaporization / Sublimation

Then the correct choice is any of the latter three (melting, vaporization, sublimation), because they all require heat input from the surroundings into the system.

Quick memory tip: If the phase change moves toward gas (or away from solid), it’s usually endothermic and absorbs heat from the surroundings.

TL;DR: The phase changes that involve heat transfer from the surroundings to the system are melting, vaporization, and sublimation.

Information gathered from public forums or data available on the internet and portrayed here.