1. Rates of Reactions Chapter 13, Section 4

2. Rates of Reactions A reaction takes place only if the particles of reactants collide. The speed at which new particles form is called the rate of reaction.

3. Activation Energy A chemical reaction needs a boost of energy before the reaction can start. Activation Energy—smallest amount of energy that molecules need to react Ex: friction, electric spark, light

4. Sources of Activation Energy… There are 4 factors that affect the rate of a reaction. 1. Temperature—higher temp=faster reaction 2. Concentration—higher conc.=faster reaction 3. Surface Area—increase S.A.=faster reaction 4. Presence of an inhibitor or catalyst

5. Inhibitor—slows down or stops a reaction Ex: preservatives added to foods to slow down growth of bacteria Catalyst—speeds up a reaction Ex: enzymes

6. Which is quicker? Step 1: Put 250mL of water into a beaker and place it on the hot plate. Step 2: Put 250mL of water into a second beaker and set it to the side. Step 3: Wait for your water on the hot plate to warm up. Step 4: Remove your beaker from the hot plate and turn it off. Step 5: Place an effervescent tablet in each one of the beakers at the same time. Time each reaction. Step 6: On your paper, record your observations for each reaction.

7. Answer the following… 1.In which beaker did the reaction occur at a faster rate? 2.Why does grinding a solid into a powder increase reaction rate? 3.Explain how chewing your food thoroughly can help your body digest food.