3.2.5.6 Catalysts
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What is a homogeneous catalysts?
Where it is in the same phase as the reactants The reaction proceeds through an intermediate species
What is a heterogeneous?
Where it is in a different phase to the reactants The reaction occurs at active sites on the surface of the catalyst
What is a phase?
The state of matter
How do heterogeneous catalysts work?
Catalytic action occurs on the solid surface which remains in place so the catalyst is not lost and does not need to be seperated from the products
How do you make heterogeneous catalysts more efficient?
Spread the catalyst on an inert support medium to increase the surface to mass ratio Increase the surface area
Why do catalysts not last forever?
The surface becomes covered with unwanted impurities which is called poisoning The finely divided catalyst may gradually be lost from the support medium
What is the catalyst for the Haber process?
Iron in the form of pea-sized lumps
What is the equation for the Haber process?
N2 (g) + 3H2 (g) =(reversible reaction)= 2NH3 (g)
What is the contact process?
It produces sulfuric acid 2SO2 + O2 = 2SO3 Catalysed by vanadium oxide (V2O5) SO2 + V2O5 = SO3 + V2O4 2V2O4 + O2 = 2V2O5
Does the destruction of the ozone layer involved a homogeneous or heterogeneous catalyst?
Homogeneous A ClO radical intermediate is formed
What are the reactions involved with I- and S2 O8(2-)?
S2O8(2-) + 2I- = 2SO4(2-) + I2 Peroxidedisulfate ions oxidises iron (II) to iron (III): S2O8(2-) + 2Fe(2+) = 2SO4(2-) + 2Fe(3+) Fe(3+) oxidies I- to I2, regenerating the Fe(2+) ions so that none are used up: 2Fe(3+) + 2I- = 2Fe(2+) + I2 Iron gives an ion to the peroxidedisulfate and takes one back from the iodide ions
What is autocatalysis?
When one of the products of the reaction is a catalyst for the reaction So the reaction starts slowly then speeds up as more product is produced