Osmotic Pressure
Osmotic Pressure
Osmotic pressure is the pressure that must be applied to stop solvent flowing across a semipermeable membrane — the basis of desalination.
The van ’t Hoff relation gives Π = M·R·T. where M is the molar concentration, R the gas constant and T temperature.
Inputs
M := 1000 mol/m^3=1000 mol/m^3
R := 8.314 J/(mol·K)=8.31 kg·m^2/K/mol/s^2
T := 298 K=298 K
Apply the van ’t Hoff osmotic-pressure relation.
p_osm := M·R·T=2.48 MPa
Results
Seawater’s osmotic pressure is around 27 bar; reverse-osmosis plants must exceed it to push fresh water through the membrane.
Assumptions & limitations
- Dilute, ideal solution.
- Fully dissociated where applicable.
- Absolute temperature.