1. 5.4 Physical and Chemical Changes
Learning Goals:
Explain a physical change
Explain a chemical change
Recognize the evidence for each type of change

2. Discussion: What’s New?
Physical or chemical change?
What is true about the kinds of matter present before and after a physical change?
How is matter different?
What substances were formed when the paper burned?
What is true about the types of matter present before and after the matter undergoes a chemical change
Would it be possible to change these types of matter back into a sheet of paper?

3. Physical Changes Change of Appearance
A physical change is a change that affects one or more physical properties of a substance.
The appearance, shape, or size of a substance may be altered during a physical change.
Physical changes, such as changes in state, do not change the chemical identity of a substance.

4. Change of Appearance
Physical Changes

5. Chemical Changes Change of Appearance
A chemical change is the process when one or more substances change into entirely new substances with different properties.
A substance’s identity changes because the chemical makeup changes.
Bonds get rearranged and/or new bonds form.
Influenced by temperature: At higher temperatures, chemical reactions happen more quickly

6. Change of Appearance

7. Look for the Signs How can you tell a chemical change has happened?
There are five key signs that a chemical reaction has occurred.
Observing two or more of these signs during a change means you are likely observing a chemical change.

8. How can you tell a chemical change has happened?
Energy that changes from one form to another can be evidence of a chemical change.
-Energy can appear as a spike or drop in temperature
- Energy can appear in the visible form of light.

9. How can you tell a chemical change has happened?
Colour changes
When a substance changes to a new colour, a chemical change has likely occurred

10. How can you tell a chemical change has happened?
Odours can be produced during a chemical change.

11. How can you tell a chemical change has happened?
The production of gas is often evidence of a chemical change.
Fizzing and foaming may mean gases are being produced.
Careful!
Boiling also can produce gas bubbles, but boiling is a physical change.

12. How can you tell a chemical change has happened?
A precipitate is a solid formed from two clear liquids being mixed together.
The formation of a precipitate can indicate a chemical change.