Question

What are the most favourable conditions to liquefy a gas?
A. High temperature and high pressure
B. Low temperature and high pressure
C. Low temperature and low pressure
D. High temperature and low pressure

Answer 1

Hint: We know that the conversion of a gas into a liquid is known as the liquefaction of gas. The intermolecular forces of attraction increase while converting a gas to a liquid. As the intermolecular forces of attraction increase the molecules come together and combine to form a liquid state.

Complete step by step solution:
Gases can be converted to liquid by cooling or compressing the gases. The gases can be liquefied by two conditions:
1. Lowering the temperature: We can convert the gas molecules to a liquid by cooling the gas molecules. As we lower the temperature of the gas molecules, the kinetic energy of the gas molecules decreases and thus, the gas molecules are converted to liquid.
2. Applying high pressure: When we apply high pressure to the gas molecules, the gas molecules get compressed. On compression, the intermolecular distance between the gas molecules decreases. As the intermolecular distance between the gas molecules decreases, the gas molecules come very close to each other and thus condense into a liquid.

In gases, the intermolecular distance is very large. But when we apply high pressure and lower the temperature the gas converts to liquid.
Thus, the most favourable conditions to liquefy a gas are high pressure and low temperature.

Thus, the correct option is (B) low temperature and high pressure.

Note:
The gas cannot be above a certain temperature irrespective of the applied pressure. This temperature is known as the critical temperature. Above the critical temperature, the kinetic energy of the gas increases and below the critical temperature, when pressure is applied the gas molecules come closer and thus, gases liquefy.