Catalysis

Question 1

Why do transition metals make good catalysts

Answer 1

Due to their variable oxidation states

Question 2

What is Haber process

Answer 2

Solid iron catalyst used to speed up reaction between hydrogen and nitrogen gases (heterogenous catalyst)

Question 3

How do transition metals speed up reaction rate

Answer 3

As electrons are transferred to produce a reactive intermediate which changes reaction pathway since enthalpy change of formation of intermediate is much lower than enthalpy change of og reaction so activation energy lower and reaction more feasible

Question 4

What is contact process and the steps of reaction

Answer 4

Uses vanadium oxide (V2O5) catalyst to speed up conversion of sulfur dioxide to sulfur trioxide
Overall: 2SO2 + O2 —->(reversible) 2SO3

Intermediate reactions:
V2O5 + SO2 —-> V2O4 + SO3
V2O4 + 1/2O2 ——> V2O5 so catalyst regenerated

Question 5

How does oxidation state of vanadium change during contact process

Answer 5

First reduced from +5 to +4 then reformed to its og oxidation state

Question 6

Why do reaction impurities lead to an increase in chemical production costs

Answer 6

As catalyst has to be replaced/cleaned regularly as poisoned by impurities which block active sites and prevent adsorption of reactants

Question 7

What impurities can poison catalyst in Haber process

Answer 7

Sulfur impurities

Question 8

Example of homogenous catalyst and intermediate reactions

Answer 8

Reaction between S2O8 2- and I- ions where Fe2+ used as catalyst

Overall: S2O8 2- + 2I- —->I2 + 2SO4 2-

Intermediate reactions:
S2O8 2- + 2Fe2+ —-> 2Fe3+ + 2SO4 2-
2Fe3+ + 2I- —-> 2Fe2+ + I2

Question 9

Why does reaction between S2O8 2- (peroxydisulfate) and I- ions need a catalyst

Answer 9

As without these negative ions would naturally repel each other and never react due to high activation energy needed to overcome repulsion