chapter 12 reaction rates and equilibrium 12.4 catalysts
TRANSCRIPT
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