Question

The critical temperature of:
(A) A substance means the temperature above which the substance is in vapour form.
(B) A gas is the temperature below which it can be liquefied by application of pressure
(C) Water is ${100^0}C$
(D) None of the above

Answer 1

Hint- In order to solve this question, we will proceed first by understanding the definition of critical temperature which states that critical temperature is the temperature at or above which the substance cannot be liquefied.

Complete answer:
> As we know that every substance has its own critical temperature for example the critical point of water is ${373.94^0}C.$
> At or above this temperature the water will not be able to liquefy whether we increase the pressure by a large amount.
> A gas’s critical temperature is a measure of the strength of the attracting intermolecular forces. The intermolecular forces are weaker, the more difficult it is to liquefy the gas and thus the critical temperature of that gas would be lower.
Hence, the correct option is B.
The critical temperature is the highest temperature at which a substance can exist as a liquid.

Note-The molecules have too much kinetic energy over critical temperature for the intermolecular attractive forces to hold them together in a separate liquid phase.
The substance instead forms a single phase that fully occupies the container's volume. Substances with strong intermolecular forces tend to form a liquid phase over a very large range of temperatures and thus have high critical temperatures. In contrast, substances with weak intermolecular interactions have critical temperatures relatively low.