Which statement best describes water vaporization energy?

Which statement best describes water vaporization energy?

• A. It requires very little energy
• B. It occurs spontaneously at room temperature
• C. It requires a large amount of energy
• D. It only occurs under high pressure

Answer: (C)

Vaporization energy is the amount of energy required to turn a liquid into a gas at a given pressure, known as the latent heat of vaporization. For water, this energy is large because molecules must break strong intermolecular forces—especially hydrogen bonds—and spread apart to occupy the larger volume of the vapor phase. When heat is added, the temperature can stay the same during the phase change while energy goes into overcoming these forces, which is why a lot of energy per mole is needed to vaporize. At room temperature, water doesn’t vaporize quickly because the energy available isn’t enough to overcome those attractions for most molecules, and vaporization only becomes significant when enough energy is supplied (boiling) or when pressure is reduced. This is why the statement describing vaporization energy as requiring a large amount of energy best captures the concept.

Vaporization energy is the amount of energy required to turn a liquid into a gas at a given pressure, known as the latent heat of vaporization. For water, this energy is large because molecules must break strong intermolecular forces—especially hydrogen bonds—and spread apart to occupy the larger volume of the vapor phase. When heat is added, the temperature can stay the same during the phase change while energy goes into overcoming these forces, which is why a lot of energy per mole is needed to vaporize. At room temperature, water doesn’t vaporize quickly because the energy available isn’t enough to overcome those attractions for most molecules, and vaporization only becomes significant when enough energy is supplied (boiling) or when pressure is reduced. This is why the statement describing vaporization energy as requiring a large amount of energy best captures the concept.