1. Warm-Up
Think critically: What do you think is happening to the movement of atoms when evaporation occurs?
Think critically: What do you think is happening to the movement of atoms when freezing occurs?
Think critically: What do you think is happening to the movement of atoms when condensation occurs?

2. What happens when there is a change in the state of matter?
Solid to liquid?
Liquid to gas?
Gas to liquid?
Liquid to solid?

3. Lets take a look for ourselves…
Ice melting lab
We will record the temperature every 30 seconds and observe what state the ice/water is in.
We will then make a graph

4. Objective: I will be able to explain how changes in state of matter require energy as evidenced by completing an ice melting lab. Phase Changes (Changes of State of Matter)

5. Explaining the States of matter
The States of matter- solid, liquid, and gas- exist because of competition between two things:
Thermal energy: energy from heat; causes molecules to vibrate and spread apart
Intermolecular forces: forces between separate atoms or molecules that are not bound together; always tries to bring molecules close
ex: hold water molecules together to make liquid water)

6. Twig
Intermolecular forces

7. So what happens during a state change? Let’s consider our lab
What type of energy did we add to the ice?
What did that cause the temperature to do at first?
Did this continue the entire lab? Why or why not?

8. Changes in State of Matter
As heat energy is added to a solid, the temperature increases until it reaches its melting point
THEN THE TEMPERATURE STOPS INCREASING. IT TAKES ENERGY TO OVERCOME INTERMOLECULAR FORCES.
As you add more heat, more of the solid becomes liquid because the heat energy is being used to break the intermolecular forces apart and change the solid to a liquid.
The heat is no longer being used to add to the temperature, therefore temperature stays the same.
Once all the solid becomes a liquid, the heat energy will then be used to raise the temperature again.

9. The temperature increases while water still exists as a liquid only
State/Phase Changes
The temperature increases while ice still exists as a solid only
The temperature increases while water still exists as a liquid only

10. Ice stays at 0oC (melting point) while it melts into a liquid
State/Phase Changes
Ice stays at 0oC (melting point) while it melts into a liquid
Liquid water stays at 100oC (boiling point) while it evaporates to a gas
During the state change, the temperature remains constant. The energy is now being used to break apart the atoms, instead of changing the temperature.

11. On a graph these changes in energy looks like…

12. Twig
Changing States of Matter

13. Lets go back
Write a scientific explanation for the following question:
What happens to the temperature during a phase change?
Claim: answer
Evidence: observations from lab/data/graph
Reasoning: explain the science we learned, why is the evidence important and do what it does?