Certified Energy Auditor Practice Exam 2026 – All-in-One Resource to Achieve Exam Success!

The phase change of water that requires the most energy and absorbs the most latent heat is the heat of vaporization. During this process, liquid water converts into water vapor. It takes a significant amount of energy—about 2260 joules per gram at 100 degrees Celsius—to overcome the hydrogen bonds that hold water molecules together in the liquid phase. This high energy requirement is due to the need for the molecules to gain enough kinetic energy to escape into the vapor phase, where they are much further apart and can move freely.

In contrast, the other phase changes, such as melting or freezing, involve less energy because they only alter the arrangement of molecules from solid to liquid or vice versa, but do not change the state to a gas. Freezing and condensation actually release energy rather than require it, as the molecules lose kinetic energy and form more structured arrangements. Thus, among the choices provided, the heat of vaporization stands out as the phase change that consumes the most energy during the transition from liquid to gas.