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Osmosis and Diffusion
Transcript of Osmosis and Diffusion
If two solutions of different concentration are separated by a semi-permeable membrane which is permeable to to the smaller solvent molecules but not to the larger solute molecules, then the solvent will tend to diffuse across the membrane from the less concentrated to the more concentrated solution.
This process is called osmosis.
Osmosis is of great importance in biological processes where the solvent is water.
The transport of water and other molecules across biological membranes is essential to many processes in living organisms. The energy which drives the process is usually discussed in terms of osmotic pressure.
If the partition is removed as in the lower illustration, the gases will mix because of the random velocities of their molecules.
In time a uniform mixture of A and B molecules will be produced in the container.
The tendency toward diffusion is very strong even at room temperature because of the high molecular velocities associated with the thermal energy of the particles.
Diffusion refers to the process by which molecules intermingle as a result of their kinetic energy of random motion. Consider two containers of gas A and B separated by a partition. The molecules of both gases are in constant motion and make numerous collisions with the partition.
Diffusion is the spontaneous net movement of particles or molecules from an area of their high concentration to an area of their low concentration through a semi-permeable membrane. For example, diffusing molecules will move randomly between areas of high and low concentration but because there are more molecules in the high concentration region, more molecules will leave the high concentration region than the low concentration one.
Diffusion is a spontaneous process. It is simply the statistical outcome of random motion. Diffusion increases entropy, decreasing Gibbs free energy, and therefore is thermodynamically favorable. Diffusion operates within the boundaries of the Second Law of Thermodynamics because it demonstrates nature's tendency to wind down, as evidenced by increasing entropy.
Therefore, there will be a net movement of molecules from high to low concentration. Initially, a concentration gradient leaves a smooth decrease in concentration from high to low which will form between the two regions. As time progresses, the gradient will grow increasingly shallow until the concentrations are equalized.