Model Answers for Worksheets of Changes of State

DIRECT READING B: CHANGES OF STATE

1. Freezing

2. Melting

3. Evaporation

4. Condensation

5. Melting

6. Endothermic

7. Freezing

8. Exothermic

9. Evaporation

10. Change of state

11. C

12. D

13. Sublimation

14. Endothermic

15. B

Review

1. The particles of a solid only vibrate. The particles of a liquid can move past one another. The particles of a gas are free to move anywhere.

2. Energy is added or removed during a change of state. A change of state does not make a new substance, so changes of state are physical changes.

3. Melting requires energy. Freezing is the removal of energy. Both happen at the same temperature.

4. Both processes change a liquid to a gas. Evaporation is a slower process than boiling. In an open container, you need to heat a liquid in order to boil it.

5. Sublimation requires energy and changes a solid directly to a gas. Condensation gives off energy and changes a gas to a liquid.

6.

Property	Solid	Liquid	Gas
Attraction between particles	strong	weaker than in a solid	little or no attraction
Distance between particles	close	close	far apart
Movement of particles	They vibrate only.	They can move past each other.	There is freedom of movement.