5: Catalysis Flashcards
What is a catalyst?
A substance that speeds up rate of reaction without being used up, by providing an alternative reaction pathway with a lower activation energy
What is a heterogenous catalyst?
A catalyst that is in a different state to the reactants
What are homogenous catalysts?
Catalysts that are in the same state as reactants
In heterogenous catalysis, what state are reactants and catalysts in?
Solid catalyst, gaseous reactant
Name the heterogenous catalyst used in the Haber process.
Iron
Give an equation for the Haber process.
N2 (g) + 3H2 (g) = 2NH3 (g)
Name the catalyst used in the contact process.
V2O3
Give an equation for the contact process.
SO2 (g) + 0.5 O2 (g) -> SO3 (g)
Where do heterogenous catalysts work during a reaction?
The reactant binds to the catalysts surface.
Explain the process of how heterogenous catalysts work.
- Reactants adsorb onto reactant surface
- Reaction take places
- Products desorbed
Give 2 issues that could happen if the heterogenous catalyst is too strong.
Reactants cannot move around the surface.
Products cannot desorb
Give 1 thing that could happen if the heterogenous catalyst is too weak.
Reactants may never adsorb.
Explain how catalytic converters are made efficient.
The catalyst is heterogenous, so is spread across the surface. Inside the catalytic converter is a honeycomb structure, increasing the surface area for attachment of the catalyst.
What is catalyst poisoning?
The active site of the catalyst becomes blocked, preventing the catalyst from binding to reactants, ruining its ability to speed up rate.
Describe how catalysts become poisoned.
Active site becomes blocked by substances that will not desorb.
Name an element that could poison the iron catalyst in the Haber process.
Sulfur
Name an element that could poison the catalyst in a catalytic converter.
Lead
What state are homogenous catalysts usually?
Aqueous
Briefly explain how homogenous catalysts work.
They form an intermediate species which reacts with products and then regenerates the original catalyst.
Describe the shape of an energy diagram showing the use of a homogenous catalyst.
The first peak shows the activation energy for the main reaction. The second peak shows the activation energy for reaction of intermediates.
Explain why the reaction of the equation shown is slow.
2I- + S2O8 2- -> I2 + 2SO4 2-
Both reactants have a negative charge and repel each other, making it unlikely that they will collide and react.
Give the ionic equation when you add an Fe2+ catalyst to this reaction.
Explain how this catalyst works to speed up rate of reaction.
2I- + S2O8 2- -> I2 + 2SO4 2-
2Fe2+ + S2O8 2- -> 2Fe3+ + 2SO4 2-
Addition of a positive ion means that there is no repulsion so particles collide and react.
Give the equation involving 2I- and 2Fe 3+ in the second stage of homogenous catalysis of S2O8 2-.
Explain what happens.
2I- + 2Fe 3+ -> 2Fe 2+ + I2
The iodide ions react with the new catalyst intermediate to produce iodine.
What is autocatalysis?
Where the product of a reaction acts as a catalyst.