Questions: Particles in Motion: Introduction to Kinetic Theory

Question 1

According to kinetic molecular theory, what happens to particle motion when temperature increases?

• A. Particles stop moving
• B. Particles move faster on average
• C. Particles get larger
• D. Particles move slower

Answer: (B)

Higher temperature means particles have more kinetic energy, so they move faster on average. This is the direct link between temperature and particle motion in kinetic theory. The particles do not change size — they just move more quickly.

Question 2

Particles in a solid are substantially still.

• T. True
• F. False

Answer: False

Particles in a solid are not still — they vibrate continuously in their fixed positions. Even though they do not move from place to place (that happens in liquids and gases), they oscillate back and forth with an amount of energy that corresponds to the temperature. Only at absolute zero would motion theoretically stop completely.

Question 3

Why does a gas fill its entire container while a liquid does not?

Model answer: Gas particles move freely at high speeds with very weak attractions between them, so they spread out to fill all available space. Liquid particles are attracted to each other strongly enough to stay close together but can slide past one another, so they take the shape of the container but do not expand to fill it.

In a gas, kinetic energy dominates over the weak attractions between particles. Particles fly in all directions, bouncing off container walls and each other, until they occupy the entire volume. In a liquid, attractions between particles are strong enough to keep them close, but not strong enough to lock them in fixed positions. This intermediate behavior gives liquids a definite volume but no definite shape.