1. Chemical Reactions
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2. Chemical Reactions Types of chemical reactions: Growing Ripen Decay
Burn
Digestion

3. Chemical Reactions Chemical reactions change substances
Sugar, water, yeast, heat  Bread
Chemical Reaction

4. Chemical Reaction
Chemical reaction - change in which one or more substances are converted into new substances
Example – baking a cake

5. Signs of Chemical Reactions
Signs a chemical reaction may have occurred:
Change in color
Production of gas
Change of identity

6. Chemical Reactions
Reactant – substance or molecule that participates in a reaction
Product – substance that forms in reaction

7. Chemical Reaction Gas in a car Reactants: Isooctane C8H18 Oxygen O2
Products:
Carbon dioxide CO2
Water H20

8. Chemical Reactions
The products and reactants contain the same types of atoms.
Rearranged as bonds are broken and formed.
Mass is always conserved

10. Energy and Reactions All chemical reactions release or absorb energy.
Takes the form of:
Heat
Light
Sound
Electricity

11. Energy and Reactions When chemical reactions take place -
Some chemical bonds in the reactants are broken
Requires energy
In order for products to be produced, new bonds must form.
Bond formation releases energy.

12. Chemical Energy
Chemical Energy – energy released when a chemical compound reacts to produce new compounds

13. Exothermic Reaction
Exothermic Reaction - The energy given off in a reaction is in the form of heat
Heat Release
Examples –
Burning wood or exploding dynamite

14. Endothermic Reaction
Endothermic Reaction - The energy needed is in the form of heat
Heat absorption
Some reactions are so endothermic that they can cause water to freeze.

15. Rate of Change Chemical reactions occur at different rates or speeds.
Explosion of nitroglycerine
Fast
Burning of carbon in charcoal
Slow

16. Reaction Rate Most reactions go faster at higher temperatures
Faster moving particles collide more often = more chance for a reaction

17. Bread in freezer vs Bread on counter

19. Rate of Reaction
A large surface area speeds up reactions

20. Rate of Reaction Concentrated solutions react faster
A drop of bleach vs a bottle of bleach

21. Rate of Reaction Reactions are faster at higher pressure
Less space = more collisions
Higher Concentration

22. Rate of Reaction Massive molecules react slower
The bigger it is the slower it moves = less collisions

23. Catalysts Catalyst – substance that changes the rate of a reaction
Speed up or slow down
Inhibitor – slows down