What are the two types of catalysts
Heterogenous and homogenous
Describe heterogenous catalysts
The catalyst is in a different state to the reactants
Describe how a heterogenous and homogenous catalyst works
- The reactant molecules are adsorbed onto the catalyst surface. This weekends bonds within the reactant molecules
- bonds within the reactant molecules break
- new bonds form making the product molecules
- the product molecules leave the catalyst surface (desorb)
Why is it important that catalysts have a large surface area?
So more collisions and more molecules can be adsorbed more frequently so the reaction can happen faster
How do catalysts work?
A catalyst speeds up the rate of a reaction without it being used up
(They do this by providing an alternative route with a lower activation energy).
Catalysts emerge chemically unchanged but may have different physical properties, e.g they may start to crumble.
Catalysts do not alter the amount of product made only the speed it is made.
What is catalysis?
The process of speeding up a reaction using a catalyst
What is a homogenous catalyst?
A catalyst in the same state as the reactants
What is cracking?
In cracking, long chain alkanes are split giving shorter chain alkanes + shorter chain alkenes
How do you crack long chain alkanes in the lab?
- in the bottom of a test tube place a piece of mineral wool soaked in your alkane, in the middle of the test tube put aluminium oxide coated broken porcelain, add a bung with a delivery tube.
- the delivery tube first goes into test tube A which collects the liquid products (5-16C)
- then the tube goes into test tube B where the gaseous products are collected over a water bath in an upturned measuring cylinder
- heat the porcelain strongly and the alkane gently
- the porcelain acts as the catalyst
- the liquid in tube A and gas in tube B can be tested for the presence of alkenes with the bromine water test
