Question

Which postulate of the kinetic molecular theory breaks down under conditions of low temperature? Explain.

Short answer

The postulate of the Kinetic Molecular Theory which assumes no attraction between particles breaks down at low temperatures, since particles have less kinetic energy, allowing intermolecular forces to become significant.

Step-by-step solution

Understanding Kinetic Molecular Theory

Kinetic Molecular Theory (KMT) explains the behavior of gases, depicting them as a large number of submicroscopic particles (atoms or molecules), all of which are in constant, random motion. The theory is based on several postulates about the nature of these particles and their motion.

Identify the Relevant Postulate

One of the postulates of KMT states that the average kinetic energy of gas particles depends on the temperature of the gas. At lower temperatures, the average kinetic energy of the particles decreases.

Recognize the Breakdown of the Postulate

Under conditions of low temperature, particles have significantly less kinetic energy, which could mean that attractive forces between particles become more prominent. This can lead to condensation or solidification, behaviors that are not accounted for in the KMT, which describes an ideal gas. Therefore, the KMT postulate that predicts no attraction or repulsion between particles (ideal gas behavior) breaks down at low temperatures.

Key concepts

Behavior of Gases

When you picture a gas, imagine it as a sea of tiny, invisible particles. These particles, whether they're atoms or molecules, are always on the move, darting around haphazardly.

Now, gases don't just wander aimlessly; they adhere to specific manners of conduct. One fascinating aspect is that they uniformly fill out any container, no matter the shape or size. Furthermore, gases can compress under pressure, which isn't something you'd typically see in solids or liquids.

The unpredictable motion of gas particles is crucial because it leads to the diffusion and mixing of different gases, even without stirring. Have you ever noticed how quickly a scent spreads in a room? That's this behavior in action!

Gas Laws

Scientists have come up with several gas laws that help to predict how a gas will react under various conditions.

For instance, Boyle's Law states that if you keep the temperature of a gas constant, and then squeeze the gas into a smaller volume, the pressure will shoot up. You've seen this in action when you press a bike pump and feel the resistance build.

Then there's Charles's Law, which tells us that if the pressure is constant but you heat the gas, it will expand and occupy more space. Imagine a balloon on a hot day swelling up - that's the law in action.

Combine these laws, and you have the Combined Gas Law that can tackle changes in pressure, volume, and temperature all at once. It's like having a master key for understanding the behavior of gases in different scenarios.

Kinetic Energy of Gas Particles

What makes gas particles zip around like little race cars? It's their kinetic energy. Kinetic energy is the driving force of their motion and it's totally dependent on temperature. The hotter the gas, the more energy its particles have, which means they move faster.

When the temperature drops, it's like taking the foot off the pedal – the particles slow down because they have less kinetic energy. This slowing down is why you might see something like steam condense into water on a cold surface. Those water particles have lost some of their go-go juice (kinetic energy) and decided to slow down and stick together.

Ideal Gas Behavior

In an ideal world, gases would follow all the rules set out by the Kinetic Molecular Theory perfectly. But remember, 'ideal' is just a concept. An ideal gas is one where the particles are so far apart that they have no effect on one another. They don't attract or repel, and they bounce off walls and each other without losing energy.

However, at low temperatures or high pressures, real gases start to veer off this ideal path. The little space between particles shrinks, and suddenly they start to feel each other's presence. They might even cozy up and form droplets of liquid. That's why, when we study gases under typical conditions, we still refer to this ideal model to make our lives simpler (even though it's not perfectly accurate).