Question

It is easier to liquefy ammonia than oxygen because (a) it is easier to compress oxygen than \(\mathrm{NH}_{3}\) (b) \(\mathrm{NH}_{3}\) has a very low critical temperature as compared to \(\mathrm{O}_{2}\) (c) \(\mathrm{O}_{2}\) has a higher value of van der Waals constant \(a\) and higher critical temperature than \(\mathrm{NH}_{3}\) (d) \(\mathrm{NH}_{3}\) has a higher value of van der Waals constant \(a\) and higher critical temperature than oxygen.

Short answer

Ammonia (h) is easier to liquefy than oxygen () because it has a higher value of van der Waals constant (a) and a higher critical temperature, as stated in option (d).

Step-by-step solution

Understanding the Question

The exercise is asking why ammonia (h) is easier to liquefy than oxygen (). The answer must be connected to the properties of these gases, especially when it comes to their liquefaction process which involves the critical temperature and the intermolecular forces represented by van der Waals constants.

Evaluating Options

Evaluate each statement given in the options:(a) Easier compression of a gas does not necessarily make it easier to liquefy.(b) A very low critical temperature for h compared to would imply that h liquefies at lower temperatures, making it easier to liquefy, which is a credible reason.(c) If had a higher van der Waals constant and critical temperature than h, it would imply stronger intermolecular forces in and potentially a higher liquefaction temperature, which does not support it being easier to liquefy than h.(d) A higher value of van der Waals constant for h and a higher critical temperature than would suggest stronger intermolecular forces and a higher temperature at which h can be liquefied, thus making it easier to liquefy.

Identifying the Correct Option

Based on the critical properties of gases, the ease of liquefaction is largely dependent on the strength of intermolecular forces and the critical temperature. Ammonia with a higher van der Waals constant has stronger intermolecular forces compared to oxygen, and it also has a higher critical temperature. This means it can be liquefied at a higher temperature and thus, more easily. Therefore, option (d) is correct.

Key concepts

Critical Temperature

The critical temperature of a gas is the highest temperature at which it can be liquefied by pressure alone. Above this temperature, no amount of pressure can change the gas into a liquid; the substance can only exist as a gas or plasma. This concept is crucial when trying to understand why certain gases are more easily liquefied than others.

Significance in Liquefaction

For a gas to be liquefied, its temperature must be below its critical temperature during the compression process. Therefore, gases with higher critical temperatures can be liquefied at higher atmospheric temperatures which is more practical in many situations. For instance, in the case of ammonia (NH_3), which has a higher critical temperature than oxygen (O_2), this implies that ammonia can be transformed into a liquid under pressure at relatively higher temperatures, making its liquefaction process more feasible in normal conditions.

Van der Waals Forces

Van der Waals forces describe a variety of intermolecular attractions such as dipole-dipole, dipole-induced dipole, and London dispersion forces. These forces are relatively weak compared to the covalent bonds within molecules but play a significant role in the phase transition of substances from gas to liquid.

Impact on Gases

The van der Waals constant 'a' in the van der Waals equation represents the magnitude of these attractive forces. A higher 'a' value indicates stronger attractions between the particles, which can lead to an easier liquefaction process since the particles are more inclined to stay close to each other, facilitating the transition to a liquid state. Ammonia, with its higher 'a' value compared to oxygen, thus exhibits stronger intermolecular attractions, aiding in its ease of liquefaction.

Intermolecular Forces

Intermolecular forces are the forces that mediate interaction between molecules, including attractions and repulsions. These forces are essential for understanding many properties of substances, such as boiling points, melting points, and capacity to be liquefied.

Types and Strengths

There are several types of intermolecular forces, from the weaker London dispersion forces to the stronger hydrogen bonds. The strength of these forces has a profound impact on how easily a gas can be liquefied. Stronger intermolecular forces result in a substance being more prone to take on a liquid form under suitable conditions. Consequently, because ammonia has stronger intermolecular forces than oxygen, as indicated by a higher van der Waals constant 'a', it will naturally have a tendency to become liquid more readily upon compression.