Catalysts - Rates of Reaction (1.2) Flashcards
How can a catalyst affect the probability of successful collisions?
Increase the probability of successful collisions
How does a catalyst affect the rate constant for a reaction?
it increases the rate constant
How can a catalyst affect the equilibrium?
Helps the system reach equilibrium more rapidly but does NOT affect the position of the equilibrium
Does a catalyst affect the enthalpy change of a reaction?
No
Does a catalyst affect the yield of a reaction?
No
Does a catalyst affect the value for the equilibrium constant?
No
What is a homogenous catalyst?
When the catalyst is in the same phase as the reactants
e.g gas/gas or liquid/liquid
What is a heterogenous catalyst?
When the catalyst is in a different phase to the reactants
Describe the process of heterogenous catalysis
- Adsorption - One of the reactants approaches the catalyst’s surface & settles onto an active site
- Another reactant approaches the catalyst
- Reaction - Re-arrangment of electrons takes place
- Deadsorption - The products are released from the surface
What must heterogenous catalysts be able to do to allow the molecules to adsorb/desorb?
The catalyst must adsorb the reactant strongly enough to enable it to react but must allow the product to desorb, otherwise the active sites will become blocked
What are good redox catalysts?
Transition metals
Why are transition metals good redox catalysts?
They have variable oxidation states and can be repeatedly oxidised & reduced
Name one of the examples of a transition metal catalysts in industry
- Iron catalyst (haber process)
- Nickel catalyst (hydrogenation of unsaturated fats)
- Vanadium catalyst (synthesis of sulphuric acid)
Name one of the examples of transition metal catalysts in biology
- Iron 2+->3+ in haemoglobin
- Cu +1->2+ in haemocyanin (O2 carrier in blue blooded species)
- Mo/Fe centres in nitrogenase (enzyme involved in nitrogen fixation)
