Question

Assertion: \[N{{H}_{3}}\] gas is more easily liquefiable than \[C{{O}_{2}}\] gas.
Reason: \[N{{H}_{3}}\] gas has higher critical temperature than \[C{{O}_{2}}\] gas.
a.) Both assertion and reason are correct and reason is the correct explanation for assertion.
b.) Both assertion and reason are correct but reason is not the correct explanation for assertion.
c.) Assertion is correct but reason is incorrect.
d.) Both assertion and reason are incorrect.

Answer 1

Hint: How easily gas will liquefy that depends on the intermolecular attraction forces, if the intermolecular attraction forces are strong, then it’s easy to liquefy the and the parameter that gives us clear idea of intermolecular attraction forces between gas particles is van der waals constant a. Higher the value of a, higher will be the intermolecular attraction forces.


Complete Solution :
\[N{{H}_{3}}\] gas is a polar gas and also hydrogen is attached to highly electronegative elements like nitrogen, so there will be hydrogen bonding between its molecule which is a strong intermolecular attraction as compared to the other van der waals forces.
- \[C{{O}_{2}}\] is a nonpolar gas as because of its linear structure, the dipole moment of one carbon-oxygen bond will be canceled out by another which makes it non-polar. Therefore the attraction forces that work between its molecules will be London dispersion forces.
So we can expect a higher value of van der waals constant ‘a’ for\[N{{H}_{3}}\] as compared to \[C{{O}_{2}}\] gas.

- Gases can be liquefied either by change in temperature or pressure. If at constant temperature we start increasing pressure then it will start bringing the gas molecules near to each-other and after a certain pressure, they will come close enough to each-other to call its physical state a liquid state. Similarly as a constant pressure if we start decreasing the temperature of the gas sample, it will decrease their energy and they will feel the effect of intermolecular attraction forces more and start coming near to each-other and at point they will come near enough to each-other to call its physical state a liquid state.

- Critical temperature is the temperature for a gas above which it can’t be liquefied by the application of pressure alone.
So, if a gas has higher critical temperature say 300 K, then below 300K it can be converted into liquid state by increasing the pressure alone and it will require less effort as compare to a gas whose critical temperature is 200 K because to liquefy that gas first of all it temperature needs to be decreased below 200 K.
- Therefore, if a gas has higher critical temperature it is easy to liquefy it.
Assertion and reason both are correct and reason is the correct explanation for assertion.
So, the correct answer is “Option A”.


Note: Critical temperature of \[N{{H}_{3}}\] is 405.5K and \[C{{O}_{2}}\] is 304.13K.
- Intermolecular attraction forces are very important for the liquefaction of a gas, that’s why you will observe that for the non-polar gases like Helium, Neon, hydrogen, oxygen etc. critical temperature is very low as compared to the polar gases like ammonia and they are much more difficult to liquefy in comparison to gases like ammonia.