1. Physical and Chemical Changes and Exothermic and Endothermic Reactions

2. Physical Change
Changes in a substance that do not alter the chemical properties of the substance
Things about the substance change, but the substance remains the same
For instance, an ice cube melts into water and you can boil that into a gas, but it remains H2O the whole time
One or more of its physical properties may be changed
Ex: change in size, shape, dissolving. possibly color change (as long as a new substance is not created)

3. Chemical Change
Changes that alter the chemical properties of a substance
A change that creates a different substance
Clues: bubbles (indicates the production of a gas), getting hot or cold, color change
Ex: iron rusting, souring of milk, burning paper

4. Endothermic and exothermic reactions
Step 1: Energy must be SUPPLIED to break chemical bonds:
Step 2: Energy is RELEASED when new chemical bonds are made:
A reaction is EXOTHERMIC if more energy is RELEASED than SUPPLIED. If more energy is SUPPLIED than is RELEASED then the reaction is ENDOTHERMIC

6. Endothermic Reactions:
a change (e.g. a chemical reaction) that requires (or absorbs) heat.
Forming Na+ and Cl- ions from NaCl is an endothermic process
Photosynthesis is an endothermic reaction (requires energy input from sun)

7. Measuring Heat
reaction
Endothermic reaction = heat taken in & temperature of the substance drops

8. Ammonium nitrate + water

9. Starting temperature 20⁰ C

10. Add ammonium nitrate to water

11. ending temperature of 12⁰ C a temperature decrease of 8⁰ C

13. Energy given out by reaction
Activation energy
Energy given out by reaction

14. a change (e.g. a chemical reaction) that releases heat.
Exothermic Reaction:
a change (e.g. a chemical reaction) that releases heat.
Burning fossil fuels is an exothermic reaction

15. Exothermic reaction = heat given off & temperature of substance rises.
Heat Released
reaction
Exothermic reaction = heat given off & temperature of substance rises.

16. Exothermic vs endothermic:
EXOTHERMIC – more energy is given out than is taken in (e.g. burning, respiration)
ENDOTHERMIC – energy is taken in but not necessarily given out (e.g. photosynthesis)
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18. Examples Exothermic Combustion of fuels Evaporation of Water
Yeast & Hydrogen Peroxide
Epsom salts & water
Endothermic
Photosynthesis
Acetic Acid & Sodium Bicarbonate
Cold Packs
Melting Ice
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19. 1. Zinc turnings are placed in a hydrochloric acid solution
Zinc - Element
HCl - compound
Bubbles indicate a gas is being produced
The Zinc seems to disappear which means its being changed into a different substance
Chemical Change
What gas do you think is being produced?

20. 2. Ripping Magnesium ribbon into pieces then ignited in a flame

21. 3. A penny is coated with zinc then heated
Copper - Element
Zinc - Element
Coating the Copper with Zinc is a physical change. Nothing new is created
Heating dissolves the Zinc and Copper to make brass. A solution of metals is called an alloy. Alloys are considered a mixture of metals and can be separated back, therefore its not a chemical change.
Normal Penny
Coated with Zinc
After being heated

22. 4. Polymers A and B are mixed
Polymer A and B are both compounds
The reaction gives off heat (exothermic), a new substance is created, therefore its a chemical reaction

23. 5. Hexane is poured down ramp and ignited
Hexane is a flammable liquid similar to methane, propane, butane, octane (chemical property)
Hexane is a compound with a low boiling point, so just exposing it to room temperature turns it into a gas (similar to nail polish remover)
The hexane vapor is denser than air so it sinks (physical property)
When its ignited, it turns into a new substance so that is a chemical change

24. 6. A styrofoam cup in acetone
Acetone - compound
Styrofoam - compound
Bonds between the polymers of the styrofoam are broken apart by the acetone
The acetone is dissolving the styrofoam
Its a physical change

25. 7. Gas bubbles are made, then ignited
The gas is methane, a compound
Gas causes the bubble to expand - physical change
Gas bubble being ignited is a chemical change