Chapter5-3: Controlling Chemical Reactions Where does the energy come from to begin to light the match?

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.

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.

a.Endothermic reactions absorb energy. -They feel cold

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.

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.

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.

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.

3. Surface Area-increasing the surface area of the reactants allows the chemical reaction to occur faster

4.Catalysts a. substance that speeds up a reaction

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.