1. Physical and chemical changes

2. First: Conservation of matter
Matter is never created or destroyed
in chemical or physical changes. 
The same number of atoms that exist
before the reaction exist after the reaction. 

3. Physical change Physical changes: Changes in energy
Changes in the state of matter.
A physical change does not produce a new substance.
Examples of physical changes include melting ice, crushing a can, melting an ice cube, and breaking a bottle.

4. Reversibility
A physical change is reversible, a chemical change is not. For example, the freezing of water is a physical change because it can be reversed.

5. Chemical changes
At the molecular level, chemical change involves making or breaking of bonds between atoms. A chemical change produces a new substance.

6. examples
Examples of chemical changes include: Combustion (burning) Rusting on a car Cooking an egg

7. Reaction = change Chemical changes are also called chemical reactions.
A chemical reaction produces a new substance with new and different physical and chemical properties. 

8. chemical change
A chemical change makes a substance that wasn't there before, while the starting and ending materials of a physical change are the same (even though they may look different). There may be clues that a chemical reaction took place:

9. 1) Composition change
During a chemical change, substances are changed into different substances. 
In other words, the composition of the substance changes.

10. 2)release or gain of energy
Another sign of a chemical change is the release or gain of energy by an object.  Many substances absorb energy to undergo a chemical change.  Energy is absorbed during chemical changes involved in cooking, like baking a cake.

11. 3) Change in odor
It only takes one experience with a rotten egg to learn that they smell different that fresh eggs.  When eggs and food spoil, they undergo a chemical change.  Skunks produce a chemical that keeps potential predators
at a distance. The change in odor is a
clue to the chemical change.

12. 4) Gas formation The formation of a gas is a clue
to chemical changes.  The bubbles
of gas that you observed form
when an antacid is dropped into
water is an example of change.

13. 5) Precipitate formed
Another clue that a chemical change has occurred is the formation of a solid.  A solid that separates out of solution during a chemical change is called a precipitate.

14. Differences?
How do physical and chemical changes differ from each other? 

15. classification
Classification of real-life processes can be tricky. Complex changes can be broken down into many simpler steps. Some of the steps are chemical and others are physical, so the overall process can't cleanly be placed in either category.
For example, boiling coffee involves chemical change (the delicate molecules that give coffee its flavor react with air and become new, bitter-tasting substances) and physical change (the water in the coffee is going from liquid to gaseous form).

16. most important
The most important thing for your to remember is that in a physical change the composition of a substance does not change and in a chemical change the composition of a substance does change.

17. Summary – Physical change
Physical Change- atoms do not rearrange into new molecules.
Physical properties change (state, shape, etc). Chemical properties do not change.
Physical changes are generally easy to reverse.

18. Summary – chemical change
Chemical change - atoms are rearranged into different molecules. There will be a new chemical formula. Both physical and chemical properties are changed. Changes are not reversible without another reaction. Energy is often produced (light, fire or heat)

19. Another take