A2- Catalysts Flashcards
Why are transition metals able to act as catalysts?
Variable oxidation states so are able to temporarily donate or accept electrons
How do catalysts speed up rate of reaction?
- Provide an alternative reaction pathway with lower Ea
- more particles have E>Ea
- more collisions lead to a reaction
What is a heterogeneous catalyst?
a catalyst in a different phase from the reactants
What is a homogeneous catalyst?
a catalyst in the same phase as the reactants
Where do reactions with catalysts occur?
at active sites on the surface
Why do active sites exist?
vacant d-orbitals that can form weak, temporary bonds
What makes a catalyst suitable?
forms strong enough bonds to adsorb reactants, but weak enough that products can de-adsorb
What is the contact process used for?
forming sulfuric acid
What catalyst is used in contact process? WHat type of catalyst is this?
V2O5 (s)
heterogeneous
Give 2 equations showing the action of V2O5 in the contact process…
V2O5 (s) + SO2 (g) –> V2O4 (s) + SO3 (g)
V2O4 (s) + 1/2O2 (g) –> V2O5 (s)
What catalyst is used in the Haber process?
Fe (s)
What is the overall equation for the Haber process?
N2 (g) + 3H2 (g) –> 2NH3 (g)
How does iron catalyse the Haber process (in 4 steps)?
1) reactants adsorb into active sites on Fe
2) bonds in reactants weaken
3) new bonds form in products
4) products de-adsorb from the surface
What is an autocatalytic reaction?
Where one of the products of the reaction catalyses the reaction
Sketch a graph of an autocatalytic reaction. Explain why it has this shape
graph is a sigmoid shape, starting on y-axis and ending on/above x-axis
- reaction rate starts slow
- catalyst increases the rate of reaction
- reaction rate decreases as reactants are used up
