What is a homogeneous catalyst?

A catalyst that has the same physical state as the reactants.


For example, sulfuric acid is a homogeneous catalyst in the production of esters because sulfuric acid and the reactants (an alcohol and a carboxylic acid) are all liquids.

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What is a heterogeneous catalyst?

A catalyst that has a different physical state from the reactants.


For example, iron is a heterogeneous catalyst in the Haber process because iron is a solid and the reactants (N2 and H2) are gases.

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Identify the type of catalyst (homogeneous or heterogeneous) in each of the following examples:

  1. Fe in the Haber process.
  2. V2O5 in the Contact process.
  3. MnO4- ions in the oxidation of ethanedioic acid.
  4. Fe2+ ions in the iodine-peroxodisulfate reaction.
  1. Fe in the Haber process - heterogeneous.
  2. V2O5 in the Contact process - heterogeneous.
  3. MnO4- ions in the oxidation of ethanedioic acid - homogeneous.
  4. Fe2+ ions in the iodine-peroxodisulfate reaction - homogeneous.

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What is catalyst poisoning, and how does it affect catalytic activity?

Catalyst poisoning refers to the accumulation of unwanted impurities on the catalyst's surface, reducing its activity.

It can lead to a decrease in catalytic efficiency and may require the replacement of the catalyst.

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What catalyst is used in the Contact process to manufacture sulfuric acid?

Vanadium(V) oxide (V2O5).

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Explain, with the use of equations, how vanadium(V) oxide catalyses the oxidation of sulfur dioxide.

  1. Vanadium(V) oxide (V2O5) oxidises sulfur dioxide to sulfur trioxide:

SO2 + V2O5 ➔ SO3 + V2O4

  1. Vanadium(V) oxide is regenerated by reaction of vanadium(IV) oxide (V2O4) with oxygen:

2V2O4 + O2 ➔ 2V2O5

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What species catalyses the reaction between S2O82- and I- ions?

Fe2+ ions

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What is meant by the term autocatalysis?

Autocatalysis refers to a situation in a chemical reaction where one of the products formed during the reaction acts as a catalyst for the same reaction.

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How does the reaction rate change in an autocatalytic reaction?

In an autocatalytic reaction, the rate increases as the reaction progresses because a product of the reaction acts as a catalyst, accelerating the reaction as it accumulates.

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Explain, with the use of half-equations, how manganese(II) ions autocatalyse the reaction between C4O42- and MnO4-.

  1. MnO4- ions oxidise Mn2+ ions to Mn3+ ions:

4Mn2+(aq) + MnO4−(aq) + 8H+(aq) ➔ 5Mn3+(aq) + 4H2O(l)

  1. Mn3+ ions oxidise C4O42- ions to produce CO2 and regenerate Mn2+ ions:

2Mn3+(aq) + C2O42−(aq) ➔ 2CO2(g) + 2Mn2+(aq)

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What catalyst is used in the Haber process to manufacture ammonia?

Iron (Fe)

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Why is the reaction between Fe2+ and I- more likely to occur than the reaction between I- and S2O82-?

 S2O82- ions are more likely to collide and react with Fe2+ ions than I- because Fe2+ and S2O82- ions have opposite charges and are attracted to each other.

When S2O82- and I- ions approach each other, more energy is needed to overcome the repulsive forces between like charges.

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Explain, with the use of equations, how Fe2+ ions catalyse the following reaction:

S2O82- + 2I- ➔ 2SO42- + I2

Fe2+ ions catalyse this reaction by participating in two redox reactions:

Reaction 1: 2Fe2+ + S2O82- ➔ 2Fe3+ + 2SO42-

Reaction 2: 2Fe3+ + 2I- ➔ 2Fe2+ + I2

These reactions involve the oxidation of Fe2+ to Fe3+ by S2O82-, and the subsequent reduction of Fe3+ back to Fe2+ by I-.


The overall reaction is catalysed by both Fe2+ and Fe3+ so the redox reactions can take in either order.

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