Question

How would you account for the following? 

Transition metals and their compounds act as catalysts.

Give a reason for the following: 

Transition elements and their compounds act as catalysts.

Explain giving reason:

Transition metals and their many compounds act as good catalysts.

Answer 1

Transition metals and their compounds are known for their catalytic activity. This property of transition metals is due to their variable valency and their ability to form complex compounds. Vanadium (V) oxide (in the contact process), finely divided iron (in the Haber process) and nickel (in catalytic hydrogenation) are some examples of catalysis by transition metals. Bonds are formed between the reactant molecules and the atoms of the catalyst surface on the solid surface of the catalyst. Metals of the first transition series use 3d and 4s electrons to form bonds, as a result of which the concentration of the reactant on the catalyst surface increases and the bonds present in the reactant molecules become weak. Due to this, the value of activation energy decreases. Transition metals are more effective as catalysts because of the possibility of changes in oxidation states.

For example, Iron (III) catalyzes the reaction between the iodide ion and the persulfate ion.

\[\ce{2I^- + S2O^{2-}_8 -> I2 ^ + 2SO^{2-}_4}\]

The explanation of this catalytic reaction is as follows:

\[\ce{2Fe^{3+} + 2I^- -> 2Fe^{2+} + I2 ^}\]

\[\ce{2Fe^{2+} + S2O^{2-}_8 -> 2Fe^{3+} + 2SO^{2-}_4}\]