1. Changes in States of Matter
7th grade Science

2. Changing states of matter
Solids can become liquids and liquids can become solids
Liquids can become gases and gases can become liquids
Solids can become gases

3. Melting – solid to liquid
Melting is the process by which a solid becomes a liquid
Melting point – is the lowest temperature at which a substance begins to melt

4. Melting and particle arrangement
As solids heat up, the particles gain energy and vibrate faster causing the particles to break loose and slide past one another becoming a liquid

5. Freezing – liquid to solid
Freezing is the process by which a liquid becomes a solid
Freezing point – is the temperature at which a specific liquid becomes a solid
The substance’s freezing point is the same as the substance’s melting point where the substance could exist either as a solid or a liquid

6. Freezing and particle arrangement
As a liquid’s temperature is lowered, the particles lose energy and move more slowly.
Eventually, the particles move so slowly that the attraction among them cause the liquid to become a solid

7. Check for Understanding
What are the ways in which a solid can change state into a liquid or that a liquid can change into a solid?

8. Evaporation – liquid to gas
Evaporation is the process by which a liquid becomes a gas
Evaporation usually occurs at the surface of a liquid
The fastest moving particles at the surface of the liquid break away from the liquid and become gas particles

9. Evaporation and particle arrangement
As the temperature increases, the energy in the liquid increases and the movement of the particles increases allowing them to escape from the liquid and become a gas

10. Boiling – liquid to gas
Boiling is another process by which a liquid becomes a gas
Boiling point – is the temperature at which the liquid becomes a gas
Substances have specific boiling points
Ex. Water boils at 100⁰C or 212⁰F

11. Check for understanding
What are the ways in which a liquid changes state into a gas? What happens to the particles during that phase change?

12. Boiling and particle arrangement
As the temperature increases, the energy in the liquid increases and the movement of the particles increases allowing them to escape from the liquid and become a gas

13. Sublimation – solid to gas
Sublimation is when a solid changes directly to a gas
Ex. Dry ice is frozen carbon dioxide that sublimates

14. Condensation – gas to liquid
Condensation is the process by which a gas becomes a liquid

15. Condensation and particle arrangement
When you cool a gas, the particles move more slowly and the attraction between the particles increases pulling the particles closer together forming a liquid

16. Check for understanding
How does sublimation differ from condensation?