Developing Fuels: Cracking Flashcards
Definition of cracking
Any reaction in which a larger molecule is made into smaller molecules
What is the catalyst for cracking
Zeolite
Possible products of cracking of alkanes (2)
- Branched alkanes + branched alkene
2. Smaller alkanes + branched alkenes
Possible products of cracking of cycloalkanes
Alkenes + branched alkenes
Possible products of cracking of alkenes
Smaller alkenes
Definition of catalyst
A substance which speeds up a reaction but can be recovered chemically unchanged at the end
Definition of catalysis
The process of speeding up a reaction using a catalyst
What are 2 rules about catalysts
- They do not affect the amount of product formed
2. They do not appear as a reactant oh the overall equation for reaction
Definition of homogenous catalysis
When the reactant and catalyst are in the same physical state (both aqueous solutions)
Example of homogeneous catalysis
Enzymes in the human body
Definition of heterogeneous catalysis
When the catalyst and reactants are in different physical states
What are the steps for heterogeneous catalysis mechanism
- Reactants get ADSORBED onto catalyst surface
- Bonds are weakened
- Bonds break
This form radicals
- New bond forms
- 2nd bond forms and product diffuses away from catalyst surface leaving it free to absorb fresh reactants
Definition of adsorbed
Chemically bound to the surface of another substance
Definition of catalyst poisoning
A substance that stops the catalyst functioning properly
Explain what happens in catalyst poisoning of heterogeneous catalysis (3)
Poison molecules are adsorbed more strongly than the reactants
= catalyst can catalyse a reaction of poison so becomes inactive,
leading to blocking of active sites by poison molecules
