Question

Why do transition metals act as good catalysts?

Hint:

A good catalyst speeds up a reaction by providing a surface or an intermediate that lowers the activation energy.

Answer 1

Concept: A good catalyst speeds up a reaction by providing a surface or an intermediate that lowers the activation energy. Transition metals are well suited to this because of their variable oxidation states and their partly filled d-orbitals.
Answer: Transition metals act as good catalysts for two main reasons. First, they show variable oxidation states, so they can easily gain or lose electrons and form unstable intermediate compounds with the reactants; this gives the reaction a lower-energy path. Second, they have partly filled d-orbitals and free valencies on their surface, which can adsorb reactant molecules, hold them close together in the right orientation, and weaken their bonds. Both effects lower the activation energy and increase the reaction rate.