Question

Explain the terms surface tension and vapour pressure.

Answer 1

Surface tension is the elastic tendency of a fluid surface which makes it acquire the least surface area possible. Surface tension allows insects, usually denser than water, to float and slide on a water surface. 
Vapour pressure:the pressure of a vapour in contact with its liquid or solid form.

Answer 2

Answer:

(1) fa volatile liquid is placed in an open vessel, the liquid molecules have a tendency to escape in a gaseous state forming vapour and difuse into surroundings. lence evaporation takes place continuously, and no equilibrium is atained.

(2) If a liquid is placed in a closed vessel, the vapour molecules get accumulated on ts Surface. These vapour molecules are n continuous random motion. They collide with each other, with walls of a container and surface of the liquid, and return to the liquid state. This reverse phenomenon is called condensation.

3) ATter some time, rates of evaporation and condensa tion become equal and an equilibrium is established between liquid and vapour phases. At this stage the vapour exerts a constant pressure called vapour pressure on iquid surface at constant temperature.

4) Vapour pressure: The pressure exerted by the vapour of a liquid (or solid) when it is in equilirium with the liquid (or solid) phase at a constant temperature is called the vapour pressure of the liquid (or solid).

(5) The vapour pressure of a hquid increases with the increase in temperature.