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# Assertion: At equilibrium, vapour phase will be always rich in the component which is more volatile.Reason: The composition of the vapour phase in equilibrium with the solution is determined by the partial pressure of the components.A) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.B) Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.C) Assertion is true but Reason is falseD) Both Assertion and Reason are false

Last updated date: 17th Jun 2024
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Hint: We know that if the vapour pressure of the liquid is high at the given temperature. We can say that the volatility of the liquid is also high but the boiling point of the liquid will be low.

We know that the mole fraction of the more volatile component is always greater in the vapour phase than in the solution phase.
We can also say that the vapour phase is comparatively richer in the component whose addition to the liquid mixture results in an increase in the total vapour pressure.
So we can say that at any fixed temperature the vapour pressure is always richer in a more volatile component as compared to the solution phase.
Hence, the Assertion statement is correct.
Let us now understand the vapour pressure:
It is known that for the solution of volatile liquid, the partial vapour pressure of the component in the solution is directly proportional to the mole fraction.
Let us take the example of the solution of volatile liquid A and volatile liquid B:
So the partial vapour pressure of component is given as follows:
${{\text{p}}_{\text{A}}}{\text{ = p}}_{\text{A}}^{\text{o}}{{t{\chi }}_{\text{A}}}$
Here, ${{\text{p}}_{\text{A}}}$ = partial pressure of vapour pressure
${\text{p}}_{\text{A}}^{\text{o}}$ = vapour pressure of pure component A
${{{\chi }}_{\text{A}}}$ = molar fraction of component A
Now we know that mole fraction of a component in the vapour phase is directly proportional to the partial pressure of that component.
And it is also known that mole fraction of a component in the vapour phase is inversely proportional to the total pressure.
Hence, the Reason statement is correct.

Therefore, we can conclude that the correct answer to this question is option A.

Note:
We can get confused between the partial vapour pressures of components in the solution phase and partial vapour pressure of components in the vapour phase. The component having the higher partial vapour phase in solution will have a greater component in the vapour phase.