Osmotic Pressure - Morse Equation

Morse Equation

The osmotic pressure Π of an ideal solution with low concentration can be approximated using the Morse equation (named after Harmon Northrop Morse):

,

where

i is the dimensionless van 't Hoff factor

M is the molarity

R=8.3145 J K-1 mol-1 (5 s.f.) is the gas constant

T is the thermodynamic (absolute) temperature

This equation gives the pressure on one side of the membrane; the total pressure on the membrane is given by the difference between the pressures on the two sides. Note the similarity of the above formula to the ideal gas law and also that osmotic pressure is not dependent on particle charge. This equation was derived by van 't Hoff.

Osmotic pressure is an important factor affecting cells. Osmoregulation is the homeostasis mechanism of an organism to reach balance in osmotic pressure.

• Hypertonicity is the presence of a solution that causes cells to shrink.
• Hypotonicity is the presence of a solution that causes cells to swell.
• Isotonic is the presence of a solution that produces no change in cell volume.

When a biological cell is in a hypotonic environment, the cell interior accumulates water, water flows across the cell membrane into the cell, causing it to expand. In plant cells, the cell wall restricts the expansion, resulting in pressure on the cell wall from within called turgor pressure.