Pakistan study notes for Matric, Intermediate, B.A, B.COM BSC, M.A, BCS. Free Pakistani Urdu educational school, colleges and University notes.



The extended kinetic molecular model accounts for most of the properties of liquids.



Like gases, liquids diffuse. One liquid may diffuse into another, e.g., a drop of a dye or any colored solution diffuses through water. Diffusions in liquids are much slower than that of gases.

In terms of molecular model, the diffusion of liquids can be explained as follows: The freedom of liquid molecules permits diffusion to take place but the closeness of molecules and resulting large number of collisions cause diffusion to be slow.


Though the liquids are not absolutely incompressible, but they may be compressed to a little extent by the high pressures. This fact leads to their use in hydraulic brake systems.


At nominal pressure, however the brake liquids can transmit the applied force to perform certain mechanical function such as braking the motions in a motor car.


In terms of molecular model, the compressibility of liquids can be explained as follows: The liquid molecules due to their closeness roll over one another. Owing to very little space the liquid molecules cannot be pushed close by pressure. Very high pressures are required for squeezing a liquid.



A liquid normally expands on heating and contracts on cooling (as does mercury or alcohol in thermometers).The molecular model explains this behavior as follows: Or heating, the kinetic energy and so the velocity of molecules increases. As a result, the volume taken by each molecule increases on heating. It results in the expansion. Contraction may similarly be explained.

The distance between liquid molecules are so small that properties of liquids are largely determined by the intermolecular attractions, Viscosity, surface tension and vapour pressure, for entrance, are not only dependent on the intermolecular forces but they are also modified with the temperature changes.

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