1. Changes in states of matter 1. The changes in the states of matter are caused by heating or cooling. For example, ice melts when it is heated and water changes into ice when it is frozen.

2. Changes in states of matter 2. The kinetic theory of matter is used to explain the changes in states of matter. Freezing  When a liquid is cooled, the particles in the liquid lose energy and move slower.

3. Changes in states of matter 2. The kinetic theory of matter is used to explain the changes in states of matter. Freezing  When a liquid is cooled, the particles in the liquid lose energy and move slower.  As the temperature continues to drop, the particles continue to lose more energy until they do not have enough energy to move freely.

4. Changes in states of matter 2. The kinetic theory of matter is used to explain the changes in states of matter. Freezing  At this point, the liquid changes into a solid.  The temperature at which this happens is called the freezing point.  Freezing point is the temperature at which a liquid changes into a solid.

5. The cooling graph of naphthalene Discussion: 2. Notice that there is a certain part of the curve where is no change in temperature with time during cooling.

6. The cooling graph of naphthalene Discussion: 2. Notice that there is a certain part of the curve where is no change in temperature with time during cooling. At this temperature, both solid and liquid are present. It is the freezing point of naphthalene (moth flakes). We call this area the plateau.

7. The cooling graph of naphthalene Discussion: (a) At point M, naphthalene exists as liquid.

8. The cooling graph of naphthalene Discussion: (b) When the liquid is cooled, the particles in the liquid lose their kinetic energy. They move slower as the temperature decreases from point M to point N.

9. The cooling graph of naphthalene Discussion: (c) At point N, liquid naphthalene begins to freeze. During the freezing process, the temperature of naphthalene remains constant because the heat loss to the surroundings is balanced by the heat energy given off during freezing. At this temperature, both solid and liquid are present.

10. The cooling graph of naphthalene Discussion: (d) At point O, all the liquid naphthalene has frozen.

11. The cooling graph of naphthalene Discussion: (e) From point O to point P, the particles in solid naphthalene release heat energy and vibrate slower. The temperature decreases from point O to point P.

12. Inter-conversion of States of Matter and Kinetic Theory of Matter 3.During the heating of naphthalene, (a) a water bath is used instead of direct heating. This is to ensure that the naphthalene is heated evenly. Furthermore, the naphthalene is flammable.

13. Inter-conversion of States of Matter and Kinetic Theory of Matter 3.During the heating of naphthalene, (b) the naphthalene is stirred continuously to ensure an even heating.