Warm-Up 10-16-17 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?

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

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

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) 10-16-17

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)

Twig Intermolecular forces

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?

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.

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

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.

On a graph these changes in energy looks like…

Twig Changing States of Matter

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?