• Created by: Emily
  • Created on: 25-05-14 12:49

Collision Theory

"Most collisions between molecules or other particles do not lead to reaction. They either don't have enough energy, or are in the wrong orientation."

Activation energy - The minimum energy that a particle needs in order to react.

Factors that decrease Ea -

  • Catalyst
  • Increasing Pressure - more reactant in a smaller space
  • Increasing Concentration - more reactant
  • Increasing Temperature - increases the kinetic energy of the particles - more collisions
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Catalyst Types

Heterogeneous catalysts

Catalyst and reactant are in a different phase eg. solid catalyst and aqueous reactant

Homogeneous catalysts

Catalyst and reactant are in the same phase

Examples & Uses

  • Catalytic converters - Platinum/Rhodium (hetero)
  • Zeolites (making petrol) - Aluminium Oxide & Silicon Oxide (hetero)
  • Hardening Fats - Nickel (hetero)
  • Making Fertilisers (Haber) - Iron (hetero)
  • Making Explosives - Platinum/Rhodium
  • Making Ethanol - H+ absorbed on solid silica & phosphoric acid (hetero)
  • Making Solvents (esterification) - H+ (homo)
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Catalytic Converters

  • Reduces levels of polluting gases in cars
  • honeycomb coated in platinum = large SA

1. Carbon monoxide + Nitroen Oxides -> Nitrogen + Carbon Dioxide

2. Hydrocarbon + Nitrogen Oxides -> Nitrogen + Carbon Dioxide + Water

First Step 

Gases form weak bonds w/ catalyst's metal atoms (absorbtion) This holds the gases in the right postition to react. Gases then react on the surface.

Second Step

Products break away from metal atoms (deabsorbtion). This creates room on the surface for more gases to react

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Zeolites & Hardening Fats


  • Minerals with open pore structure = ions & molecules fit into these
  • Confine molecules in small spaces = change structure and reactivity
  • Widely used as catalysts for petrochemical industry (cracking)

Hardening Fats

  • Hydrogenation of saturated fats -> unsaturated fats eg. margarine
  • Bubble Hydrogen into liquid fat w/ Nickel
  • C2H4 + H2 --> C2H6
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Ozone Layer

CFCs escape into the atmosphere and stay there because they are so relatively unreactive.

They do eventually decompose

O3 + O --> 2O2

Cholrine atoms are used as catalysts

Nitrogen Oxides so the same thing as CFCs

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