Catalyst

Question 1

Why TM can acts as catalyst

Answer 1

Provide alternative reaction pathway with low Ea

Question 2

Why TM can behave as homogeneous catalyst?

Answer 2

Variable OS;

Gain or loss e readily;

Speed up rn through e transfer

Question 3

Why TM acts as heterogeneous catalyst

Answer 3

Partially filled or empty d-orbitals;

Form temporary bonds with rxt molecules;

Provide surface for rn to occur

Question 4

Outline the mode of action of homogeneous catalyst (description)

Answer 4

S2O82- + 2I- -> 2SO42- + I2

Uncatalysed rn, direct rn bt two similarity charged ions;

Electrostatic repulsion bt the two negatively charged ions cause reactions to have high Ea

Question 5

Outline the mode of action of homogeneous catalyst (equations)

Answer 5

Step1: 2Fe3+ + 2I- -> 2Fe2+ + I2

Step2: 2Fe2+ + S2O82- -> 2Fe3+ + 2SO42-

Oppositely charged ions having natural tendency to attract each other;

Lowering Ea and enhances reaction rates

Question 6

Explain the mode of action of heterogeneous catalysis (description)

Answer 6

Reactants (N2 g and H2 g) adsorbed onto the active sites of Fe(s) catalyst;

Weakening the bonds in reactants;

Lowering Ea;

Surface conc of rxtants increases;

Rn then occurs bt reactants are close to each other and in correct orientation;

After the pdt is formed, desorb from the surface of catalyst

Question 7

Outline the mode of action of heterogeneous catalyst (equations)

Answer 7

N2(g) + 3H2(g) -> 2NH3(g)

Fe(s)

Question 8

Eg of homogeneous catalysed rn

Answer 8

Oxidation of amphoteric SO2 by oxides of N from car exhaust fumes

Question 9

Explain the reactions in catalytic converters

Answer 9

Oxides of N reduced to N2 by xsCO present, Rh acting as catalyst;

CO oxidised to CO2, Pt and Pd as catalyst;

Unburnt hydrocarbon oxidised to CO2 and H2O with Pt and Pd as catalyst