Changes of State d. Students know the states of matter (solid, liquid, gas) depend on molecular motion. e. Students know that in solids the atoms are closely locked in position and can only vibrate; in liquids the atoms and molecules are more loosely connected and can collide with and move past one another; and in gases the atoms and molecules are free to move

How do the particles in a solid substance change when energy is added? 1. Solid to Liquid Changing from Solid to Liquid requires an increase of thermal energy. How do the particles in a solid substance change when energy is added? They vibrate faster! Energy causes particles to move faster and faster until they break from their fixed positions.

Are freezing and melting chemical or physical changes? Melting (Solid to Liquid) When a substance melts, the __________ in the solid vibrate so fast that they break free from their _________ positions. Most pure substances have a specific melting point. Melting point of water is 0 degrees Celsius Freezing (Liquid to Solid) When a substance freezes, the __________ in the liquid move so slowly that they begin to take on __________ positions. Freezing point of water is 0 degrees Celsius Are freezing and melting chemical or physical changes?

How did the gold become liquid? How did the gold become a brick? It’s not just water that goes through the process of freezing and melting. . . How did the gold become liquid? How did the gold become a brick?

2. Liquid to Gas Vaporization Evaporation (Liquid to Gas) Particles in a liquid gain enough __________ to move ______________. Motion of molecules increases. Two kinds of vaporization: Evaporation (Liquid to Gas) Occurs on the surface of a liquid Boiling (Liquid to Gas) Occurs at the surface AND below the surface Boiling point of water = 100 degrees Celsius

Boiling Throughout the liquid Evaporation Added energy allow SOME of the molecules on the surface to escape

2. Liquid to Gas Condensation (Gas to Liquid) Reverse of Vaporization What happens? The particles in a gas lose enough thermal energy to form a liquid. The gas particles cool down (lose energy). They can no longer overcome the attractive forces between them. Freedom of motion decreases