Name: Gay Lussac's and Avogadro's Law
Uploaded: 2019-07-19
Duration: 18 min 33 s
Description: The video beautifully explains the two laws for an easy understanding of the students. Gay Lussac's law and Avogadro's law are explained here. Watch and learn.

Question

Briefly explain the term “vapour pressure”. What are the factors on which the vapour pressure of a liquid depends ?

Accepted Answer

Definition :
The pressure exerted by the vapour pressure above the liquid in equilibrium with the liquid at any temperature is called Vapour Pressure.
Vapour Pressure :
According to kinetic theory of liquids, the molecules of liquids are in a state of constant motion in different direction and with different speeds. Due to which liquids molecules possess different Kinetic energies. At any temperature, the molecules present at the bulk may overcome the force of attraction by neighbouring molecules and may come in the space above the liquid as the time will pass; more and more liquid molecules leave the liquid (bulk) and come in the space above the liquid. There molecules that are present above the liquids are called vapour.
The vapour molecules are also in a state of constant motion and collide with one another and with the walls of the container. Due to these collisions, the vapour molecules exert some pressure on the walls of the container. This pressure exerted by the vapour is known as vapour pressure.

Factors affecting vapour pressure:
(1) Nature of liquid
The Vapour pressure of a liquid depends upon the nature of liquid. It is dependent on intermolecular forces of attraction among the molecules of a liquid. If intermolecular forces of attraction in a liquid are weak, then molecules can easily leave the liquid and come into the vapour phase. Hence, the vapour pressure of that liquid is higher.

(2) Effect of temperature
The vapour pressure of a liquid is highly dependent on the temperature.
With the increases in temperature, the fraction of molecules having larger kinetic energy increases. Therefore, more molecules escape from the surface of liquid. As a result, the concentration of molecules in the vapour phase will increase. Hence, the vapour pressure of the liquid increases. This can also be explained on the basis of Maxwell’s distribution of energies.
At a particular temperature, energy accessed by all molecules is not same. Only those molecules, whose kinetic energy is more than $E$ , can escape from liquid into vapour phase. With increases in temperature, there is a shift in curve and number of molecules escaping the molecules also increases.

Briefly explain the term “vapour pressure”. What are the factors on which the vapour pressure of a liquid depends ?

Important Questions on States of Matter: Gases and Liquids

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