Phases of Matter, Thermal Equilibrium, and Heat Transfer

Matter commonly exists in three phases, solid, liquid, and gas, and can move between them through phase changes driven by energy transfer. Melting is the change from solid to liquid, and freezing is the reverse. Vaporization (boiling or evaporation) is the change from liquid to gas, and condensation is the reverse. Sublimation is the direct change from solid to gas, seen in materials such as dry ice and iodine. Each of these transitions involves either absorbing energy to weaken bonds or releasing energy as bonds re-form, and each occurs at characteristic temperatures for a given pressure.

A key distinction exists between evaporation and boiling, both of which turn a liquid into a gas. Boiling occurs throughout a liquid at a single fixed temperature, the boiling point, where bubbles of vap