1. Chemical Reactions

2. In order for a chemical change to occur, there has to be a reaction first that will produce that change. The law of conservation of mass states: Atoms are neither created, nor destroyed, during any chemical reaction, just rearranged.

3. Every reaction involves energy. A reaction either absorbs energy or releases energy.

4. Endothermic Reaction An endothermic reaction is a chemical reaction in which energy is absorbed. Cold to the touch “Endo” means “go in” “Thermic” means “heat” or “energy”.

5. Ammonium thiocyanate is mixed with barium hydroxide. The mixture is stirred and the two solids react. A slush is formed because water is one of the products of the reaction. A drop of water is placed on a block of wood and the beaker is placed on the water drop. The reaction is endothermic, that is, it takes in heat. As a result, the bottom of the beaker becomes cold enough to freeze the water and stick to the wood.

6. Exothermic Reaction An exothermic reaction is a chemical reaction in which energy is released. Feels hot to the touch. “Exo” means “go out” or “exit” “Thermic” means “heat” or “energy”

7. Exothermic Reactions

8. Reactants and Products All reactions involve reactants and products. Reactants are the substances you start with. Products are what is produced.

9. 2Na + Cl 2NaCl In the equation above, you start with reactants, Na and Cl (on the left side of the equation). NaCl and heat are the products (on the right side of the equation). Because of a reaction, you NOW have a change!!!

10. Rates of Reactions The rate of a reaction is a measure of how quickly the reaction takes place.

11. Four factors that affect the rate of a reaction…. Temperature Concentration Surface area of reactants Catalyst or inhibitor

12. Temperature A higher temperature means a faster rate of reaction. Example: fireworks

13. Concentration Generally, a higher concentration of reactants means a faster rate of reaction. Example: Crowded shopping mall when you are bumping into people.

14. Surface Area When the surface area, or the amount of exposed surface, of solid reactants is greater, the rate of reaction is faster. Example: Cornstarch Cannon

15. Catalyst A catalyst is a substance that speeds up a reaction without being permanently changed. Example: Enzymes in the body that breakdown food for digestion.

16. Inhibitor An inhibitor is a substance that slows down or stops a chemical reaction. Example: Preservatives slow down reactions, so food will not spoil.