DF5 Flashcards
What is cracking?
Any reaction in which a larger molecule is made into smaller molecules.
What is catalytic cracking?
Fuel is heated in the presence of a catalyst.
What are some types of cracking reactions?
alkanes →branched alkanes + branched alkenes
alkanes → smaller alkanes + cycloalkanes
cycloalkanes → alkenes + branched alkenes
alkenes → smaller alkenes
What is a problem with catalytic cracking?
Coke forms on the catalyst surface so that the catalyst eventually becomes inactive. So the catalyst needs to be regenerated.
What is a catalyst?
A substance which speeds up a reaction but can be recovered chemically unchanged at the end.
What is catalysis?
The process of speeding up a chemical reaction using a catalyst.
What does a catalyst affect?
Doesn’t affect the amount of product formed, only the rate at which it is formed.
What is a homogeneous catalysis?
Where both the reactants and catalyst are in the same physical state.
What is a heterogeneous catalysis?
Where the catalyst and reactants are in different physical states.
Where does a reaction occur when a solid catalyst is used?
On the surface of the catalyst.
How does a reaction occur on the surface of a solid catalyst?
- Adsorption - reactants form bonds with atoms on surface of catalyst.
- Bonds in reactant molecules are weakened and break.
- New bonds form between reactants - forming products.
- This weakens bonds to catalyst surface, so products released.
What are the heterogeneous catalysts made of in (industrial processes)?
They are transition metals or transition metal compounds.
What is a catalyst poison?
A substance that stops a catalyst functioning properly.
How does catalyst poisoning occur in heterogeneous catalysis?
- Poisoned molecules are adsorbed more strongly to catalyst surface.
- Catalyst cannot catalyse a reaction of the poison so becomes inactive.
- Poison molecules block active sites.
