Question

It is easier to liquefy oxygen than hydrogen because:
A. Oxygen has a higher critical temperature and lower inversion temperature than hydrogen.
B. Oxygen has a lower critical temperature and higher inversion temperature than hydrogen.
C. Oxygen has a higher critical temperature and higher inversion temperature than hydrogen.
D. The critical temperature and inversion temperature of oxygen is very low.

Answer 1

Hint: The liquefaction of gases is made easier if the critical temperature is high, since the gas can be liquified at a wider range of pressure. Also, high inversion temperatures favour liquefaction. Both these temperatures are related to the intermolecular forces of attraction between the gas particles.

Complete step by step answer:
Let us first understand what is critical temperature and liquefaction :
Critical temperature is the temperature above which a substance cannot exist as a liquid, however high the pressure is. Above this temperature, the kinetic energy of the gas particles would be so high that no amount of pressure applied will make them come together in order to get liquified.
Liquefying a gas can occur by two means: either we can keep increasing the pressure so that the gas particles come closer and closer, or we can reduce the temperature so that the velocity of the gas particles get lowered and they come together. Therefore, higher critical temperatures are favoured for liquefaction because then, we wouldn’t need to spend more energy in order to bring down the temperature to the critical temperature.
Inversion temperature is the temperature above which the gas heats up when expanded, and below which it cools down when expanded. Thus, for liquefaction, higher inversion temperatures are favourable since we’re trying to compress the gas into a liquid, and not expand it.
Now, when we compare hydrogen and oxygen, hydrogen is a lighter gas, meaning that it has weaker intermolecular forces than oxygen. As a result, molecules are further apart in hydrogen and hence, have lower critical and inversion temperatures than oxygen.
Therefore, as we have seen from above, liquefaction is made easier for oxygen as it has higher critical and inversion temperatures.

So, the correct answer is Option C.

Note: At low inversion temperatures, when temperature is lower than it, the gas expands on cooling, meaning that it heats up when we try to compress it. This is unfavourable as we want the temperature to also reduce so that it can easily become a liquid. In other words, the gas must be below its inversion temperature in order for the liquefaction to happen easily. Note that the phenomenon which explains this increase/decrease in gases during expansion is known as the Joule-Thompson effect.