Unit 7: Reaction Rates and Equilibrium

Aim 7.5: How do catalysts increase reaction rate?

Do now: Complete the review questions at the top of the handout.

Do Now:

a) What is the potential energy of the reactants of the forward reaction? _______ kJ

b) What is the potential energy of the products of the forward reaction? _____kJ

c) What is the activation energy of the forward reaction? _______kJ

d) Calculate the heat of reaction for the forward reaction. _______kJ

Catalysts – substances that increase the rate of a chemical reaction by lowering the activation energy. Catalysts provide an alternate pathway for the reaction. They are not reactants in the actual reaction.

(1) What does the catalyst called lactase do in the small intestine of humans?

(2) Why do adults who do not produce lactase experience gas, bloating, and diarrhea when they eat dairy products containing lactose?

Catalysts provide an alternate pathway for reactants, meaning that they hold them together so they have the correct orientation needed for an effective collision.

1. How does a catalyst change the activation energy (Ea) of a reaction?

2. How does a catalyst change the potential energy (PE) of the reactants and products?

3. In what way does a catalyst change the rate of a chemical reaction?

4. The diagram on the right shows an uncatalyzed reaction. Draw a dotted line to show how the activation energy would be different in the catalyzed reaction.

Lab #15: The Catalytic Decomposition of Hydrogen Peroxide (H2O2) by Catalase

In our lab, we will add potatoes to the hydrogen peroxide because potatoes contain a catalyst called catalase that increases the rate of this reaction.

We will determine the rate of the reaction by measuring the amount of bubbles produced.

The faster the bubbles are produced, the faster the enzyme molecules are breaking down the H2O2 molecules and the faster the reaction is taking place.

Check for understanding: What is the name of the catalyst molecule found in potatoes? ___________________ Hypothesis: Which tube do you think will have the fastest reaction? _____________ Why?

Directions:

1. Put 6-8 mL of room temperature hydrogen peroxide (H2O2) into the PINK test tube. 2. Put 6-8 mL of cold hydrogen peroxide (H2O2) into the ORANGE test tube. 3. Measure and record the initial temperature of both test tubes. 4. Get 6 potato pieces from the front of the room. 5. Place 3 pieces into each test tube and record the start time. 6. Six minutes later, measure and record the final temperatures. Also measure and record the height of the foam. 7. Calculate the change in temperature and record your observations.