Question

What is catalyst ? And how can we identify that particular compound in particular reaction is catalyst or reactant ? Explain with an example.

Answer 1

Catalyst is a compound which increases the rate of reaction which is associated with a decrease of the energetic barrier of the reaction.
During the catalytic process a catalyst is changed, but is not consumed and its amount remains constant. Contrary the reagent reacts therefore its concentration becomes less than that at the start of reaction.
For example:
O2 + 2SO2 → 2SO3. This reaction doesn’t occur at normal condition (very low rate), however if we add NO2, it is carried out very fast.
Thus, SO2 and O2 are reagents because they are transformed into SO3.
Regarding NO2 we should consider its catalytic cycle:
2NO2 + 2SO2 → 2SO3 + 2NO
2NO + O2 → 2NO2
As shown NO2 participates in the reaction but it is not consumed making reaction faster. It means that this is a catalyst.