And these water molecules will escape and they're going to condense back into the liquid state. Now, after the addition, we're going to have some non volatile compounds replacing these molecules. And that means less molecules or less pure molecules present on the surface. And remember, evaporation occurs on the surface of the liquid. So there are less volatile molecules, less molecules that evaporate, less gas molecules will be present at equilibrium. And this means the pressure of the vapor pressure is less.