Osmosis

:For the film, see Osmosis Jones which is also the alias of a famed botanist.

Osmotic pressure

As mentioned before, osmosis can be opposed by increasing the pressure in the region of high solute concentration with respect to that in the low solute concentration region. The force per unit area required to prevent the passage of water through a selectively-permeable membrane and into a solution of greater concentration is equivalent to the osmotic pressure of the solution, or turgor. Osmotic pressure is a colligative property, meaning that the property depends on the concentration of the solute but not on its identity.

Related Topics:
Force - Solution - Turgor - Colligative property

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Increasing the pressure increases the chemical potential of the system in proportion to the molar volume (deltamu = delta PV). Therefore, osmosis stops, when the increase in potential due to pressure equals the potential decrease from Equation 1, i.e.:

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:delta PV = -RT ln(1-x_2)qquad (2)

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Where delta P is the osmotic pressure and V is the molar volume of the solvent.

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For the case of very low solute concentrations, -ln(1-x_2) ≈ x_2 and Equation 2 can be rearranged into the following expression for osmotic pressure:

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:delta P = RTx_2/V qquad (3)

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