Membrane allows solvent molecules to pass but not solute molecules. If membrane separates solution from another solution, solvent passes into solution with higher solute concentration, because more solvent molecules hit membrane on side with less solute and pass through to other side {osmosis}|.
For example, solvent can be water, with many solute molecules inside membrane bag. See Figure 1.
pressure
Osmosis increases solvent amount on membrane side with higher solute concentration, causing extra pressure on that membrane side. The osmotic pressure resists further osmosis, because number of solvent molecules hitting both membrane sides becomes equal.
For example, water passes into bag, making bag bigger and stretching it. Membrane is under pressure. The extra water inside causes higher pressure inside, meaning more water molecules hit membrane inside. See Figure 2.
chemical potential
Mixtures have higher chemical potential than pure liquids, so pure liquid goes from pure-liquid membrane side to mixture membrane side, raises liquid level on mixture side, and lowers chemical potential. Chemical-potential decrease generates osmotic pressure, which tries to bring system into equilibrium.
small solutes
Membrane can allow small solute molecules and ions to pass through, but not large solute molecules. Small molecules diffuse through membrane, tending to make small-solute molecule concentrations equal on both membrane sides.
Physical Sciences>Chemistry>Inorganic>Phase>Solution>Osmosis
5-Chemistry-Inorganic-Phase-Solution-Osmosis
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Date Modified: 2022.0224