Section 2.2

1. Section 2.2 CHANGES OF STATE ARE PHYSICAL CHANGES

2. II. Solids can become liquids, and liquids can become solids • Examples of solids that can change to liquids • Ice melts into water • Others???

3. A. Melting • Melting is the process of a solid becoming a liquid • Different solids melt at different temperatures • Energy is GAINED making the particles move FASTER • Melting point is the lowest temperature at which a substance melts • Substances with a well-defined melting point have an orderly structure

4. B. Freezing • Freezing is the process of a liquid becoming a solid • many substances are “frozen” at room temperature • Energy is LOST making the particles move SLOWER • Freezing point is the temp. at which a liquid becomes a solid • Freezing point of a substance equals the melting point of that same substance

5. A. Evaporation • Evaporation is the process of a liquid becoming a gas • Usually occurs at the surface • Solids can lose particles at the surface, similar to liquids, by the process of sublimation • Energy is GAINED making the particles move FASTER

6. B. Boiling • Boiling is the process of changing a liquid to a gas by producing bubbles which contain dissolved air • Can occur only when a certain temp. has been reached which is called the boiling point • The boiling point of water at higher elevations is lower because of lower air pressure

7. B. Boiling (continued) • Different substances have different boiling points a) Helium boils at -270°C (-454°F) b) Aluminum boils at 2519°C (4566°F) • Energy is GAINED making the particles move FASTER

8. C. Condensation • Condensation is process by which a gas becomes a liquid • Energy is LOST making the particles move SLOWER • Like evaporation, condensation occurs over a wide range of temperatures