CHEMISTRY · Single correct · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
Liquid water is introduced into an evacuated, rigid container and allowed to stand at constant temperature. After several minutes, the vapor pressure inside the container stops changing. Which of the following best explains the constancy of the vapor pressure at this point?
(a) The water vapor now occupies the entire volume of the container, and because there is no room for additional molecules, the pressure can no longer rise.
(b) The rates of evaporation and condensation have become equal, so the number of vapor molecules remains constant.
(c) All of the liquid water has evaporated, leaving no further source of molecules to increase the pressure.
(d) Once the air above the liquid becomes saturated (100 % relative humidity), evaporation stops and only condensation occurs.