Transition metals - catalysis Flashcards
Definition of a catalyst
Substance that increases the rate of chemical reaction but is not used up
Name the two types of catalyst
Homogenous and heterogenous
What is heterogenous catalyst
Catalyst in a different phase to the reactants
Three stages of hetereogenous catalyst q
Adsorbsion
Reaction
Deadsorbsion
Explain the three stages of a heterogenous catalyst
One reactant adsorbs onto surface of catalyst - bonding at the active site
- adosrbsion concentrates recatants together making collision more likely
- adsorbsion may weaken bonds in reactats making reaction easier
- adsorbsion positions reactant particles in favourable orientation
products deadsorb
what happens if adorbsion is too weak
not many molecules adsorbed so catalyst has little effect
what happens if adsorption is too strong
molecules can’t move around active sites so are less likely to meet reactant particles and react
what is catalyst poisioning
where other substances adsorb strongly to catalysts, blocking their active sites
Name two examples of catalyst poisoning
Lead poisoning of platinum catalytic converters
Sulphur poisioning of Fe catalyst in haber process (from S impurities in H2 natural gas)
What is the equation and catalyst for the contact process
2SO2 + o2 >< 2SO3
V2O5 catalyst
Write equations for catalysis by vanadium oxide in the contact process
v2o5 + so2 > V2o4 + SO3
V2O4 + 1/2O2 > V2O5
So2 + 1/2o2 > SO3
What is a homogenous catalyst
Catalyst in the same phase as the reactants
Reaction and catalyst for haber process
3H2 + N2 > 2NH3
Fe catalyst
explain, with the aid of equations, how Fe2+ ions catalyse the reaction between I− and S2O82–
overall
2I- + [S2O8]2- > I2 + 2[SO4]2-
reaction is slow because it involves reaction of two negatively charged species which repel each other
in the catalysis of the reaction Fe2+ reduces S2O8 to SO4 and is oxidised to Fe3+
Fe3+ then oxidises I- to I2, being reduced to Fe2+
explain, with the aid of equations, how Mn2+ ions autocatalyse the reaction between C2O42– and MnO4–
Reaction is slow until some Mn2+ is formed which the catalyses the reaction
Mn2+ reduces MnO4- to Mn3+
Mn3+ oxidises [C2O4]2- to CO2, reforming Mn2+
2MnO4- +16H+ + 5[C2O4]2- > 2Mn2+ + 8H2O + 10CO2