Which of the following pairs of phase changes is endothermic?
melting and freezing
vaporization and melting
sublimation and condensation
deposition and vaporization
freezing and condensation
Solution: An endothermic reaction absorbs heat while an exothermic reaction releases heat. As solid turns into liquid (melting) and liquid turns into gas (vaporization), heat is absorbed. Heat is released when gas turns into liquid (condensation) and liquid turns into solid (freezing). Choice B is the correct answer.