Liquids with high saturation vapor pressure evaporate _______ those with lower saturation vapor pressure.

• A. Faster than
• B. At the same rate as
• C. Slower than
• D. Not at all

Answer: (A)

At a given temperature, how readily a liquid evaporates is tied to its saturation vapor pressure. A liquid with high saturation vapor pressure has more molecules at the surface with enough energy to escape into the vapor phase. That makes the net flux of molecules leaving the liquid larger, so it evaporates faster than a liquid with a lower saturation vapor pressure. In other words, higher vapor pressure means higher volatility, so the evaporation rate is greater under the same conditions. The idea that it would be slower, the same rate, or not at all doesn’t match how vapor pressure reflects a liquid’s tendency to enter the vapor phase. For example, acetone evaporates quickly at room temperature because its saturation vapor pressure is high, unlike water, which has a lower saturation vapor pressure and evaporates more slowly.