SECTION 2: CHANGES OF STATE Chapter 2: Solids, Liquids, and Gases

Changes Between Solid and Liquid Melting  Solid to liquid  Increase in thermal energy  Point at which melting occurs is called melting point  At melting point, particles of a solid are vibrating so fast that they break free from their fixed position  During melting, any energy continues to change the arrangement of the particles so the temperature does not increase

Melting

Checkpoint 1 Describe what happens to ice when it reaches 0 o C.

Checkpoint 1 Describe what happens to ice when it reaches 0 o C. The molecules of water vibrate until they can break free from the crystal structure.

Changes Between Solid and Liquid Freezing  Liquid to solid  Reverse of melting  Loss of energy  Freezing point=melting point  At freezing point, particles of a liquid move so slowly that they begin to form a regular pattern  During freezing, any loss of energy contributes to change in arrangement of molecules so temperature does not decrease

Changes Between Solid and Liquid

Changes Between Liquid and Gas Vaporization  Liquid to gas  Takes place when particles in a liquid gain enough energy to form a gas  Two main types:  Evaporation: takes place only on the surface when particles gain enough energy to escape into the air  Boiling: when a liquid changes to a gas below its surface as well as at the surface Boiling point: temperature at which liquid boils Affected by pressure: lower pressure lower boiling point

Vaporization

Checkpoint 2 Both evaporation and boiling are changes from liquid to gas. How are they different?

Checkpoint 2 Both evaporation and boiling are changes from liquid to gas. How are they different? Evaporation only takes place on the surface of a liquid. Boiling takes place both on and below the surface.

Changes Between Liquid and Gas Condensation  Gas to liquid  Opposite of vaporization  Occurs when particles in a gas lose enough thermal energy to form a liquid  Ex. Formation of clouds and rain; “sweat” on glass on hot day; fogging up a window with your breath

Condensation

Changes Between Solid and Gas Sublimation  Solid to gas  Particles of a solid do not pass through the liquid state as they form a gas  Ex. Dry ice (frozen carbon dioxide)

Particles Are Like People If you heat up a crowded room, people will start to become agitated and move away from one another, just like particles in a container

Summary Diagram

Checkpoint 3 Which phase change goes directly from solid to gas?

Checkpoint 3 Which phase change goes directly from solid to gas? Sublimation

Post-lesson Quiz 1. If a substance has a melting point of 50 o C what is its freezing point? a. 100 o C b. 25 o C c. 75 o C d. 50 o C

Post-lesson Quiz 2. Which phase change occurs when a gas becomes a liquid? a. condensation b. melting c. freezing d. sublimation

Post-lesson Quiz 3. What happens to particles when heat is added? a. they move faster and further apart b. they move faster and closer together c. they move slower and further apart d. they move slower and closer together

Post-lesson Quiz 4. Which phase change occurs when a liquid becomes a gas? a. melting b. freezing c. vaporization d. condensation

Post-lesson Quiz 5. What happens to boiling point when pressure decreases? a. It stays the same. b. There is not enough information to know. c. It increases. d. It decreases.