A summary of topic 9, organised so the notes are easy to understand. The notes are on slides, so they can be printed out and used as revision cards or posters, for revision on the go. The notes cross-reference the specification so it is easy to see where each bit of information has come from. They ...
Collision theory: Homogeneous catalysts:
= for a reaction to take place particles must collide with the = catalyst in same state as reactants
correct orientation and an energy>/=Ea (successful collision) E.g. acidified potassium dichromate in organic mechanisms
Rate of reaction: Heterogeneous catalysts:
= change in [reactants or products] / time = catalyst in a different state to reactants
From a graph = gradient of tangent E.g. haber process
To increase rate: N2 (g) + 3H2 (g) ⇌ 2NH3 (g) cat = Fe(s)
↑ temp How heterogeneous catalysts work:
- ↑ rate = ↑ KE ∴faster ∴↑successful collisions 1. ADsorption - reactants adsorb onto catalyst surface by
- ↑particles have E>Ea ∴↑successful collisions forming bonds with the catalyst
↑ conc 2. Reaction - bonds in reactants break (due to new
- ↑ likely to collide ∴↑successful collisions strong bonds formed w/ catalyst) & product formed
↑ pressure 3. Desorption - product leaves catalyst surface
- ↑ likely to collide ∴↑successful collisions Poisoning = blocking active sites - adsorb and wont desorb
↑ SA (solids) Catalytic converters
- ↑ particles available to collide∴↑successful collisions = thin metal catalyst coating & honeycomb structure to ↑ SA
+ catalyst and ↓ metal used
- Lowers Ea ∴↑particles have E>Ea ∴↑successful - Use Pt ot rhodium catalysts (expensive)
collisions Remove CO & NO from vehicle exhausts:
1. 2NO → N2 + O2
2. O2 + 2CO → 2CO2
∴ 2NO + 2CO → N2 + 2CO2
Catalysts:
← reaction profile
Catalysts provide
alternative routes that
have a lower Ea.
They ↑ rate = products are
made faster ∴ saves time
and money
Also ↑ rate = no need for ↑
heat (saves fuel) ∴
reduces pollution
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