Which statement is not a characteristic of liquefaction by compression and cooling?

• A. Occurs at high pressure and low temperature
• B. Involves removal of heat
• C. Involves condensation of gas into liquid
• D. Occurs spontaneously at room temperature and pressure

Answer: (D)

Liquefaction by compression and cooling relies on making a gas dense and cold enough that its molecules can come together and form a liquid. Pushing the gas to high pressure increases density, while removing heat lowers the molecules’ kinetic energy, allowing intermolecular attractions to dominate and the gas to condense. So this process involves high pressure, removal of heat, and condensation of gas into a liquid.

What doesn’t fit is the idea that liquefaction happens spontaneously at room temperature and pressure. Under ambient conditions, most gases have too much energy and are not near their condensation point, so you don’t get a phase change without applying cooling and/or significant compression.