Low temperature and high pressure
Explanation
The state of matter is determined by the balance between intermolecular forces of attraction (which tend to keep molecules together) and thermal energy (which tends to keep them apart). Liquefaction is the process of converting a gas into a liquid by manipulating these factors.
Analysis of Conditions:
- Effect of Temperature: High temperatures correspond to high kinetic energy, causing gas molecules to move rapidly and overcome attractive forces. To liquefy a gas, the kinetic energy must be reduced so that intermolecular forces can bind the molecules together. Therefore, low temperature is required.
- Effect of Pressure: In the gaseous state, molecules are widely separated. Increasing pressure compresses the gas, reducing the distance between molecules. When molecules are brought sufficiently close, intermolecular forces of attraction become significant, facilitating the transition to the liquid state. Therefore, high pressure is required.
Consequently, the combination of low temperature (to reduce kinetic energy) and high pressure (to bring molecules closer) creates the most favorable conditions for the liquefaction of a gas.
Key Takeaway:
Gases are most easily liquefied when the intermolecular forces of attraction are maximized through high pressure and the disruptive thermal energy is minimized through low temperature.