The vertical panel to the right of the two-compartment system is a "strip-chart recorder" that plots the osmotic pressure of the simulation (along the horizontal dimension) as a function of time (along the vertical dimension). Note that when the compartment contains equal solute concentrations, the pressure oscillates around the middle of the chart; this is the zero pressure position. When osmosis occurs into the right-hand compartment, a "negative" pressure (to the left of the zero line) is generated to prevent diffusion from occurring. Alternatively, osmosis from right to right requires a "positive" pressure on the left-hand compartment to prevent it from expanding. Thus, all pressures are measured relative to the left-hand compartment in this simulation.
For several different simulations plot the pressure values as a function of the difference in solute concentration, and describe the relationship.
A precise quantitative relationship between osmotic pressure (pi) and solute concentration (C), the gas constant (R), and the absolute temperature -<pi = CRT> - was worked out in the last century by the Dutch chemist v'ant Hoff. Go on to the next page to explore this relationship.