1. Section 3: Controlling Chemical Reactions Objectives: explain that every chemical reaction requires activation energy to get started list factors that control the rate of chemical reactions Where does the energy come from to begin to light the match?

2. I. Getting Reactions Started A.Activation energy 1. energy needed to start a chemical reaction. Here the friction of striking a match heats the substances on the match, breaking bonds in the reactant.

3. B. Endothermic reactions needs a supply of energy to keep it going. 1.The energy level of the product materials is higher than the starting reactant materials.

4. a. Endothermic reactions absorb energy.

5. C.Exothermic reactions do not require additional energy to complete the reaction. 1.Energy level of product materials is lower than the energy level of the reactants materials.

6. II. Rates of Chemical Reactions: A. Factors affecting rates of reactions: 1.Concentration a. the amount of one material in a given amount of another material Bubbles of hydrogen form when magnesium reacts with an acid. The test tube on the left has a lower concentration of acid than the test tube on the right.

7. 2.Temperature a. increasing or decreasing temperature can control the rate of a reaction. The light stick on the right glows brighter than the one on the left because the higher temperature causes the rate of the reaction to increase.

8. OR Chemical reactions can be slowed down by decreasing the temperature. Refrigerated food does not spoil as quickly because the cool temperatures slow down the chemical reactions of bacteria.

9. 3. Surface Area The concrete wall of this grain elevator in Kansas were blown apart by an explosion when grain particles and oxygen above the stored wheat exploded. Grain dust has a much greater surface area exposed to air than the top surface of the pile of grain does.

10. 4.Catalysts a. substance that speeds up a reaction without being permanently changed. Hydrogen peroxide slowly decomposes to form water and oxygen. A. manganese dioxide, the black powder, speeds up this reaction, causing bubbles to form faster. B. Since it is not used in the reaction, MnO 2 is a catalyst.

11. Catalytic converter This catalytic converter contains platinum and palladium-two catalysts that increase the rate of reactions that make the car’s exhaust less polluting.

12. 5.Inhibitor a. substance that slows down or stops a chemical reaction. Chemical preservatives are added to foods to inhibit or slow spoilage from bacteria and mold.