Transition metals - catalysis

Question 1

Definition of a catalyst

Answer 1

Substance that increases the rate of chemical reaction but is not used up

Question 2

Name the two types of catalyst

Answer 2

Homogenous and heterogenous

Question 3

What is heterogenous catalyst

Answer 3

Catalyst in a different phase to the reactants

Question 4

Three stages of hetereogenous catalyst q

Answer 4

Adsorbsion
Reaction
Deadsorbsion

Question 5

Explain the three stages of a heterogenous catalyst

Answer 5

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

Question 6

what happens if adorbsion is too weak

Answer 6

not many molecules adsorbed so catalyst has little effect

Question 7

what happens if adsorption is too strong

Answer 7

molecules can’t move around active sites so are less likely to meet reactant particles and react

Question 8

what is catalyst poisioning

Answer 8

where other substances adsorb strongly to catalysts, blocking their active sites

Question 9

Name two examples of catalyst poisoning

Answer 9

Lead poisoning of platinum catalytic converters

Sulphur poisioning of Fe catalyst in haber process (from S impurities in H2 natural gas)

Question 10

What is the equation and catalyst for the contact process

Answer 10

2SO2 + o2 >< 2SO3
V2O5 catalyst

Question 11

Write equations for catalysis by vanadium oxide in the contact process

Answer 11

v2o5 + so2 > V2o4 + SO3
V2O4 + 1/2O2 > V2O5
So2 + 1/2o2 > SO3

Question 12

What is a homogenous catalyst

Answer 12

Catalyst in the same phase as the reactants

Question 13

Reaction and catalyst for haber process

Answer 13

3H2 + N2 > 2NH3
Fe catalyst

Question 14

explain, with the aid of equations, how Fe2+ ions catalyse the reaction between I− and S2O82–

Answer 14

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+

Question 15

explain, with the aid of equations, how Mn2+ ions autocatalyse the reaction between C2O42– and MnO4–

Answer 15

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