CHAPTER 12 Reaction Rates and Equilibrium 12.4 Catalysts

2 Reaction profile activation energy, E a : the minimum amount of energy required for molecules to react. Reactants Products Reaction: A + B → C + D ∆H < 0 If E a is very high, the reaction might take place very slowly or not take place at all

Catalysts Reaction: A + B → C + D ∆H < 0 Catalysts are substances that lower the energy barrier Catalysts are not consumed during the reaction and can be reused

Catalysts catalyst: a substance that speeds up the rate of a chemical reaction by providing a pathway with a lower activation energy. Reaction: A + B → C + D ∆H < 0 Catalysts work by providing a new pathway with a lower activation energy Biological catalysts are called enzymes

Catalysts Enzymes H 2 O(l) + CO 2 (g) → H + (aq) + HCO 3– (aq) Carbonic anhydrase (enzyme) Carbonic anhydrase helps to remove CO 2 from your tissues by dissolving it in the form of HCO 3–.

Catalysts Enzymes H 2 O(l) + CO 2 (g) → H + (aq) + HCO 3– (aq) Carbonic anhydrase (enzyme) Carbonic anhydrase helps to remove CO 2 from your tissues by dissolving it in the form of HCO 3–. Saliva contains carbonic anhydrase. The tingling sensation comes from the acid H + when it touches the nerve endings on your tongue

Catalysts Enzymes Gelatin is a protein made from collagen The gelatin is able to hold its shape

Catalysts Enzymes Gelatin is a protein made from collagen The gelatin is able to hold its shape The gelatin never polymerizes (“sets”) when pineapple is added… Why?

Catalysts Enzymes Gelatin is a protein made from collagen Pineapple contains an enzyme called bromelain, that helps “break down” protein Without the bonds responsible for protein structure, the protein in gelatin cannot hold together. The gelatin never polymerizes (“sets”) when pineapple is added…

Catalysts Catalysts and the environment Ozone (O 3 ) protects us from harmful radiation from the sun. The natural ozone cycle (in the stratosphere) occurs as follows: O 3 (g) + UV(radiation) → O + O 2 (g) O + O 2 (g) → O 3 (g) How O 3 is replenished

Catalysts Catalysts and the environment Ozone (O 3 ) protects us from harmful radiation from the sun. The natural ozone cycle (in the stratosphere) occurs as follows: O 3 (g) + UV(radiation) → O + O 2 (g) O + O 2 (g) → O 3 (g) How O 3 is replenished What happens when chlorofluorocarbons (CFCs) are present? Freon–11Freon–12 used in air conditioning systems, aerosols and in the manufacture of Styrofoam™products

Catalysts O 3 (g) + UV(radiation) → O + O 2 (g) O + O 2 (g) → O 3 (g) How O 3 is replenished Natural ozone cycle: Ozone depletion mechanism: Cl(g) + O 3 (g) → ClO(g) + O 2 (g) O + ClO(g) → Cl + O 2 (g) O + O 3 (g) → 2O 2 (g) Step 1: Step 2: Overall: O 3 is not replenished ClO is an intermediate Cl is not consumed; it is a catalyst. Catalysts and the environment

Catalysts Freon–11Freon–12 used in air conditioning systems, aerosols and in the manufacture of Styrofoam™products Ozone depletion mechanism: Cl(g) + O 3 (g) → ClO(g) + O 2 (g) O + ClO(g) → Cl + O 2 (g) O + O 3 (g) → 2O 2 (g) Step 1: Step 2: Overall: O 3 is not replenished In 1996, the manufacture of freon was banned with a 10-year grace period for developing countries Catalysts and the environment

Catalysts Catalysts are important Catalysts are important because: Without catalysts, the only way to speed up a reaction is by raising the temperature, which is not always possible or safe

Catalysts Catalysts are important Catalysts are important because: Without catalysts, the only way to speed up a reaction is by raising the temperature, which is not always possible or safe Society depends on the high speed production of chemicals used for food, shelter and clothing

Catalysts Catalysts are important Catalysts are important because: Without catalysts, the only way to speed up a reaction is by raising the temperature, which is not always possible or safe Society depends on the high speed production of chemicals used for food, shelter and clothing Environmental chemists can use catalysts to reduce the amount of high- level pollutants; Los Angeles was the first city to mandate the use of catalytic converters on cars

Catalysts Catalysts are important Catalysts are important because: Without catalysts, the only way to speed up a reaction is by raising the temperature, which is not always possible or safe Society depends on the high speed production of chemicals used for food, shelter and clothing Environmental chemists can use catalysts to reduce the amount of high- level pollutants; Los Angeles was the first city to mandate the use of catalytic converters on cars Living organisms (including humans) would not exist without enzymes

Catalysts Reaction: A + B → C + D ∆H < 0 Catalysts are substances that lower the energy barrier Catalysts are not consumed during the reaction and can be reused Biological catalysts are called enzymes