Question

Under what two conditions are gas molecules unable to overcome the weak attractive forces that exist between them?

Short answer

The two conditions under which gas molecules are unable to overcome the weak attractive forces between them are: 1. Low temperature: At sufficiently low temperatures, the average kinetic energy of gas molecules decreases, causing the molecules to have a lower speed and be unable to overcome the weak attractive forces between them. This may lead to condensation into liquid or solid phases. 2. High pressure: High pressure results in a higher concentration of gas molecules and closer proximity to one another, making the weak attractive forces more significant. If the pressure is high enough, these forces can overpower the kinetic energy of the gas molecules, causing the gas to condense into a liquid or solid phase.

Step-by-step solution

Condition 1: Low Temperature

When the temperature of a gas decreases, the average kinetic energy of the gas molecules also decreases. As a result, the average speed of the gas molecules is lower. At sufficiently low temperatures, the kinetic energy of the gas molecules becomes too low for them to overcome the weak attractive forces between them. At this point, the gas molecules will start to condense into liquid or solid phases. For example, at extremely low temperatures, gases like nitrogen and oxygen will solidify.

Condition 2: High Pressure

High pressure results in a higher concentration of gas molecules, meaning they are in closer proximity to one another. When gas molecules are close together, the weak attractive forces between them become more significant. If the pressure is high enough, these forces can overpower the kinetic energy of the gas molecules, causing the gas to condense into a liquid or solid phase. For example, under high pressure, even gases like carbon dioxide and propane can be compressed into liquid forms.

Key concepts

Low Temperature Effects on Gases

When discussing the impacts of temperature on gases, it's crucial to understand that temperature is directly related to the kinetic energy of gas molecules. As the temperature of a gas drops, so does the energy these tiny particles possess.

This decrease in energy leads to a reduction in the speed at which gas molecules move. In practical terms, think of gas molecules as tiny, hyperactive children who gradually lose their energy as the temperature drops, moving less and less until they can barely tug on each other.

At very low temperatures, this lack of movement allows the weak but ever-present attractive forces between the molecules, known as van der Waals forces, to gain the upper hand, encouraging the molecules to snuggle close together and eventually coalesce into liquid or solid forms. This process is central to understanding how things like liquid nitrogen or solid carbon dioxide—commonly known as dry ice—come into existence.

High Pressure and Gases

Increasing the pressure on a gas is somewhat akin to forcing a large group of people into an elevator; the closer they get, the more likely they are to interact. Similarly, as pressure mounts, gas molecules are compelled to be in closer quarters, enhancing the likelihood of their weak attractive forces taking effect.

Under high pressure, these forces can trigger a phase change, pulling gas molecules together to form a liquid or even a solid. This principle underlies how carbon dioxide can be sold in tanks as a liquid or how propane is stored in portable containers for use in grills or heaters. The technology behind refrigeration and air conditioning also relies heavily on manipulating pressure to achieve the desired temperature effects on gases.

Kinetic Energy in Gas Molecules

The concept of kinetic energy is central to the behavior of gas molecules. Kinetic energy is essentially the energy of motion. The more kinetic energy gas molecules have, the faster they move, and the stronger they are at resisting the attractions pulling them together.

Imagine gas molecules as buzzing bees, zipping around at high speeds. Their rapid movement represents high kinetic energy. This energy helps them overcome their natural attraction to one another, similar to how bees too busy flying around don't clump together. In the world of gases, temperature is the nectar that fuels the bees; the hotter it is, the faster they move and the less likely they are to settle down into liquid or solid formations.

Understanding kinetic energy helps explain why increasing temperature generally causes gases to expand while cooling them leads to condensation and possibly solidification.