Osmosis and Osmotic Pressure

Osmosis describes the mechanism of the net movement of molecules of water due to diffusion between different concentration areas. As a solution is segregated from liquid water by a differentially permeable membrane or semipermeable membrane, the pure water appears to join the solution by osmosis. Today, the pressure needed to prevent water from osmotically entering a solution is called osmotic pressure.

Osmotic pressure can also be defined as the pressure a solution would generate when enclosed in an osmometer and allowed to come to equilibrium with pure water. Osmotic pressure of a solution depends on the number of solvent and solute molecules. The more concentrated a solution, the greater is its osmotic pressure. From the definition of osmotic pressure, it is clear that there is no actual pressure exerted by a solution except when the solution is enclosed in an osmometer.

Types of Nuclear Reactions

An example of a nuclear reaction is natural radioactive decay. Other examples of nuclear reactions include the bombardment of target nuclei with subatomic particles to artificially induce radioactivity called nuclear fission and the nuclear fusion of small nuclei at extremely high temperatures. Rutherford’s transmutation of nitrogen and Cockcroft and Walton’s fission of lithium are both particular examples of what is generally termed “nuclear reactions”.

Not only do nuclear reactions produce new nuclei and other subatomic particles but they also require energy absorption or emission. According to Einstein’s theorem, nuclear reaction must preserve total energy such that changes in mass are followed by changes in energy. The two important nuclear reactions are

  • Nuclear fission – Nuclear fission is the splitting of heavy nuclei into two or lighter nuclei with a release of a huge amount of energy in the form of nuclear energy.
  • Nuclear fusion – Nuclear fusion is the combination of two or lighter nuclei to form a heavy nucleus of a huge amount of energy in the form of nuclear energy. The released energy is called the mass defect.

Measurement of Osmotic Pressure

An osmometer is used to calculate osmotic strain and uses one or more of the solution’s colligative properties. These depend on the osmolarity and are depression of freezing point, the elevation of boiling point, reduction in vapor pressure and exertion of osmotic pressure. Osmometers can utilize the fact either that 1 ol of a solute, which is added to 1kg of water will depress the freezing point by 1.86oC or that the molar concentration of a solute causes a directly proportional reduction in the vapor pressure of the solvent. 

The can’t Hoff equation is based on the recognition that dilutes solutions behave in a similar way to gases,


Osmotic Pressure = n[(number of particles) x (concentration /molecular weight)] x R(universal gas constant) x T(absolute temperature)

Since osmotic pressure is only a potential pressure, nowadays scientists prefer to use the term osmotic potential, which is equivalent to osmotic pressure but is given a negative sign.

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