What do you understand by vapour pressure? Discuss factors affecting it.

Que.: What do you understand by vapour pressure? Discuss factors affecting it.

Ans.:

Vapour Pressure:

When a liquid is placed in an open vessel, it evaporates. The molecules of a liquid move with different kinetic energies. Those molecules which possess higher kinetic energies manage to overcome the intermolecular forces holding them in a liquid and thus escape from the liquid surface as vapours. The process by which the molecules of a liquid go into the gaseous state is called vaporisation or evaporation.

If the liquid is placed in a closed vessel, the vapours escape into the empty spaces above the liquid but as the concentration of the liquid molecules in the empty spaces increases the molecules strike on the walls of the vessel and get converted back into liquid. This process is called as condensation. Thus a dynamic equilibrium is established between the liquid and vapour at a given temperature. Now the concentration of the vapour in. the space above the liquid remains unchanged with the lapse of time. This vapour will exert a definite pressure at equilibrium. The pressure exerted by the vapour in equilibrium with the liquid is called as vapour pressure.

Factors affecting vapour pressure:

Factors affecting vapour pressure are discussed as follows:

Nature of the liquid: The vapour pressure exerted by a liquid depends on its nature. Liquids with a low boiling point will have a high vapour pressure.

Intermolecular forces of attraction: Liquids with weak intermolecular forces of attraction evaporate faster and then have a high vapour pressure.

Temperature: If the temperature of the liquid increases, the vapour pressure also increases. An increase, in temperature increases the kinetic energies of more molecules and hence more of them leave the liquid thereby increasing the vapour pressure.

Que.: What do you understand by vapour pressure? Discuss factors affecting it.