The next figure shows two beakers, one containing pure water and one containing an aqueous glucose solution, in a sealed chamber. We can view the system as having two competing equilibria: water vapor will condense in both beakers at the same rate, but water molecules will evaporate more slowly from the glucose solution because fewer water molecules are at the surface. Eventually all of the water will evaporate from the beaker containing the liquid with the higher vapor pressure (pure water) and condense in the beaker containing the liquid with the lower vapor pressure (the glucose solution). If the system consisted of only a beaker of water inside a sealed container, equilibrium between the liquid and vapor would be achieved rather rapidly, and the amount of liquid water in the beaker would remain constant.
Net water transfer
2. How does solute concentration impacts the rate (speed) of net transfer of water? Explain.
The rate of net transfer of water between two solutions is impacted by the concentration of solute in the solution. In the case of the glucose solution, the presence of glucose molecules in the solution reduces the number of water molecules at the surface of the liquid. This results in a lower vapor pressure for the glucose solution compared to pure water. As a result, water molecules will evaporate more slowly from the glucose solution compared to pure water.
The lower vapor pressure of the glucose solution means that fewer water molecules will evaporate from the solution, leading to a slower rate of net transfer of water from the glucose solution to the pure water solution. In other words, the concentration of solute in the solution affects the equilibrium between the liquid and vapor phases, resulting in a slower rate of net transfer of water in the presence of a solute.
Overall, the presence of solute in a solution reduces the rate of net transfer of water between two solutions by affecting the vapor pressure and hence the equilibrium between the liquid and vapor phases.