Question

A chemist is studying the properties of a gas under various conditions. He observes that when the gas is at room temperature and low pressure, it behaves as an ideal gas. When the gas is cooled to 10 kelvin (–263ºC) and is placed under high pressure, however, it deviates significantly from an ideal gas. There are multiple reasons for this phenomenon. Check all of the correct reasons below.

The ideal gas model assumes that gas particles experience no intermolecular attractions and these forces cause the gas to deviate from ideal behavior.

At very low temperatures, gas particles move slowly.

At very high pressures, gas particles are very close together.

Gases placed under high pressure will undergo deposition, changing from a gas to a solid.

Answer 1

Correct choices: the first three statements. Explanations:

- The ideal gas model does assume no intermolecular attractions (and point-sized particles). Real intermolecular forces (and finite molecular volume) cause deviations from ideal behavior — especially when particles are close or moving slowly.

- At very low temperatures particles have much lower kinetic energy and move more slowly, so attractive forces are relatively more important and the gas deviates from ideality.

- At very high pressures particles are forced close together, making finite molecular volume and intermolecular forces important, again causing nonideal behavior.

Why the fourth is wrong: high pressure alone does not necessarily produce deposition (gas → solid). Phase changes depend on both pressure and temperature and on the substance; typically gases condense to liquids before freezing, and deposition only occurs under specific conditions.