An inflated balloon shrinks when placed in a freezer because the

Analysis

This question tests your understanding of the Kinetic Molecular Theory of Gases and Charles’s Law, which describes the relationship between the temperature and volume of a gas.

Concept Explanation

The Kinetic Molecular Theory states that gas particles are in constant, random motion. The temperature of a gas is a measure of the average kinetic energy (the speed) of these particles.

• At higher temperatures: Gas particles move faster and collide with the walls of the container more frequently and with greater force, exerting higher pressure.
• At lower temperatures (like in a freezer): The kinetic energy of the gas particles decreases, meaning they move more slowly. Because they are moving slower, they collide with the walls of the balloon less frequently and with less force.

According to Charles's Law, for a fixed amount of gas at constant pressure, the volume of the gas is directly proportional to its absolute temperature ($V \propto T$). When you lower the temperature, the volume must decrease to maintain the balance between the internal pressure of the gas and the external atmospheric pressure.

Step-by-Step Solution

1. Identify the change: Placing the balloon in a freezer decreases the temperature of the gas trapped inside.
2. Analyze the effect on particles: As temperature drops, the kinetic energy of the gas molecules decreases.
3. Relate to pressure: Slower-moving molecules strike the inner surface of the balloon with less force and frequency, resulting in a decrease in the pressure exerted by the gas on the balloon walls.
4. Result: Because the internal pressure drops, the constant external atmospheric pressure pushes the balloon inward, causing it to shrink until the internal and external pressures equalize again.

Evaluating the Options

• A: Incorrect. Volume decreases, not increases, when temperature drops.
• B: Incorrect. The number of gas molecules remains the same; they are just moving differently.
• C: Correct. The reduction in gas motion leads to fewer and weaker collisions, reducing the pressure and allowing the balloon to shrink.
• D: Incorrect. Gas molecules only stop moving completely at Absolute Zero (0 Kelvin), which is not achieved in a standard freezer.

Exam Tip

Whenever you see a question about gas laws, remember the "Collision Rule": Temperature is speed. High temperature = fast particles = more collisions = higher pressure/volume. Low temperature = slow particles = fewer collisions = lower pressure/volume.