CHAPTER 12

Reaction Rates and

Equilibrium

12.4 Catalysts

2 12.4 Catalysts

Reaction profile

activation energy, Ea: the minimum amount of energy required for molecules to react.

Reactants

Products

Reaction: A + B → C + D ∆H < 0

If Ea is very high,

the reaction mighttake place very slowlyor not take place at all

3 12.4 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

4 12.4 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 < 0Catalysts work by providing a new pathway with a lower

activation energy

Biological catalysts are called enzymes

5 12.4 Catalysts

Enzymes

H2O(l) + CO2(g) → H+(aq) + HCO3– (aq)

Carbonic anhydrase(enzyme)

Carbonic anhydrase helps to remove CO2 from your tissues by dissolving

it in the form of HCO3–.

6 12.4 Catalysts

Enzymes

H2O(l) + CO2(g) → H+(aq) + HCO3– (aq)

Carbonic anhydrase(enzyme)

Carbonic anhydrase helps to remove CO2 from your tissues by dissolving

it in the form of HCO3–.

Saliva contains carbonic anhydrase. The tingling sensation comes from the acid H+ when it touches the nerve endings on your tongue

7 12.4 Catalysts

Enzymes

Gelatin is a protein made from collagen

The gelatin is able to hold its shape

8 12.4 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?

9 12.4 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…

10 12.4 Catalysts

Catalysts and the environment

Ozone (O3) protects us from harmful radiation from the sun.

The natural ozone cycle (in the stratosphere) occurs as follows:

O3(g) + UV(radiation) → O• + O2(g)

O• + O2(g) → O3(g)How O3 is replenished

11 12.4 Catalysts

Catalysts and the environment

Ozone (O3) protects us from harmful radiation from the sun.

The natural ozone cycle (in the stratosphere) occurs as follows:

O3(g) + UV(radiation) → O• + O2(g)

O• + O2(g) → O3(g)How O3 is replenished

What happens when chlorofluorocarbons (CFCs) are present?

Freon–11 Freon–12

used in air conditioning systems, aerosols and in the manufacture of Styrofoam™products

12 12.4 Catalysts

O3(g) + UV(radiation) → O• + O2(g)

O• + O2(g) → O3(g)How O3 is replenished

Natural ozone cycle:

Ozone depletion mechanism:

Cl(g) + O3(g) → ClO(g) + O2(g)

O• + ClO(g) → Cl • + O2(g)

O• + O3(g) → 2O2(g)

Step 1: Step 2:

Overall: O3 is not replenished

ClO is an intermediateCl is not consumed; it is a catalyst.

Catalysts and the environment

13 12.4 Catalysts

Freon–11 Freon–12

used in air conditioning systems, aerosols and in the manufacture of Styrofoam™products

Ozone depletion mechanism:

Cl(g) + O3(g) → ClO(g) + O2(g)

O• + ClO(g) → Cl • + O2(g)

O• + O3(g) → 2O2(g)

Step 1: Step 2:

Overall: O3 is not replenished

In 1996, the manufacture of freon was banned with a 10-year grace period for developing countries

Catalysts and the environment

14 12.4 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

15 12.4 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

16 12.4 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

17 12.4 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

18 12.4 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