[10.2] catalysts Flashcards
draw the energy profile diagrams for a reaction with and without a catalyst
for both exothermic and endothermic, activation energy should be lower (ie. peak of curve is lower)
what is a catalyst?
a substance that increases the rate of a chemical reaction without being used up in the process by providing an alternative route for the reaction with lower activation energy
what are the two types of catalysis?
- homogeneous catalysis
- heterogeneous catalysis
homogeneous catalysis
- catalyst and reactants are in the same physical state
- catalyst reacts with the reactants for form an intermediate
- intermediate breaks down to give product
- catalyst is regenerated
what are some examples of homogeneous catalysis?
esterification:
- conc. sulfuric acid (l) catalyses the reaction between acids and alcohols
- CH₃COOH (l) + C₂H₅OH (l) ⇌ CH₃COOC₂H₅ (l) + H₂O (l)
ozone (O₃) depletion:
- Cl● radicals as catalyst
- 2O₃ (g) ⇌ 3O₂ (g)
heterogeneous catalysis
- catalysts are in a different physical state to the reactants
- eg. solid catalyst in gaseous reaction
- 3 step process
describe the process of heterogeneous catalysis [3]
1) adsorption - species lands on active site and forms bonds with catalyst. may use some bonding electrons in the molecules, weakening them and making a subsequent reaction easier
2 and 3) reaction - adsorbed gases are held on surface in right orientation for reaction to occur. this increases chances of favourable collisions taking place
4) desorption - re-arrangement of electrons, products are released from active site
industrial processes involving heterogeneous catalysts (4)
making ammonia (haber process):
- Fe (s) catalyst
- N₂ (g) + 3H₂ (g) ⇌ 2NH₃ (g)
reforming:
- Pt (s) or Rh (s) catalyst
- C₆H₁₄ (g) -> C₆H₁₂ (g) + H₂ (g)
hydrogenation of alkenes:
- Ni (s) catalyst
- C₂H₄ (g) + H₂ (g) -> C₂H₆ (g)
making sulfur trioxide for sulfuric acid (contact process)
- V₂O₅ (s) catalyst
- 2SO₂ (g) + O₂ (g) ⇌ 2SO₃ (g)
what are catalytic converters?
- convert harmful reactants into less harmful products
- 2CO (g) + 2NO (g) -> 2CO₂ (g) + N₂ (g)
catalysis - sustainability and economic importance
- lowers the temperature and energy needed
- less energy means less fossil fuels used
- reduced carbon dioxide emissions
what is autolysis?
a reaction product that acts as a catalyst for that reaction
why are catalysts useful? (9)
- catalysts are not used up in a reaction
- reactions take place at lower temperatures with lower energy demand
- lower activation energy
- use less fuel
- less carbon dioxide emitted into atmosphere
- fossil fuels last longer
- different reactions can be used with less waste
- less hazardous chemicals
- catalysts or enzymes can generate specific products
