📚 Part 1: Multiple Choice

1. Which state of matter has particles closely packed in fixed positions?

A) Solid

B) Liquid

C) Gas

D) Plasma

2. Which scenario shows particles moving fastest (greatest average speed)?

A) Ice at 0°C

B) Water at 20°C

C) Steam at 100°C

D) Liquid nitrogen at −196°C

3. When a liquid is heated until it boils, the particles mainly:

A) Move more slowly and come closer together

B) Move faster and spread further apart

C) Stop moving completely

D) Become electrically charged

4. Which change will increase the density of a gas in a cylinder (same amount of gas)?

A) Heating the gas at constant volume

B) Cooling the gas at constant volume

C) Compressing the gas (reducing volume)

D) Adding more energy without changing volume

✏️ Part 2: Short Answers & Activities

5. Draw the particle arrangement for a gas in a container. Show particle motion with arrows.

6. In 2–3 sentences, explain how diffusion provides evidence for the particle model.

7. Which is denser: ice at 0°C or liquid water at 20°C? Briefly explain why using particle ideas.

8. If a metal rod is heated, what happens to the spacing between its particles and the length of the rod? Explain in one sentence.

9. Match each term with the correct description. Draw a line between matching items.

1. Diffusion

2. Density

3. Thermal expansion

4. Compressibility

A. How much mass is in a given volume

B. Particles spread from high to low concentration

C. Volume increases when temperature rises

D. How easily volume decreases when pressure is applied

10. Practical: A fixed amount of gas in a syringe is cooled from 25°C to 5°C while volume stays the same. What happens to the pressure and why? (One sentence)

✅ Answers

1. A) Solid

2. C) Steam at 100°C

3. B) Move faster and spread further apart

4. C) Compressing the gas (reducing volume)

5. Example answer: Particles far apart, random positions, arrows showing fast motion in all directions.

6. Example answer: Diffusion occurs because particles are constantly moving and gradually spread from regions of high concentration to low concentration, showing particles move independently.

7. Liquid water at 20°C is denser than ice at 0°C because ice particles form a more open structure (more space between particles) while liquid particles are closer together.

8. Particles vibrate more and move slightly further apart, so the rod typically becomes longer (thermal expansion).

9. 1–B, 2–A, 3–C, 4–D

10. The pressure decreases because cooling slows particle motion so particles collide with the walls less often and with less force.