Autocatalytic Reaction is the reaction where a product itself acts as a catalyst for the reaction. It can act as a catalyst for the same reaction or the coupled reaction. It increases the rate of the reaction.
Catalysts are the substances, which increase the rate of the reaction but remain unchanged themselves. Berzelius coined the term catalyst.
A self catalysed reaction by one of the products is referred to as an autocatalytic reaction. In this type of reaction, initially, the rate of reaction is very slow but when the reaction proceeds and products are formed then the rate of the reaction increases. Here the product catalyses the self-production.
An autocatalytic reaction can be expressed as A + B ⇌ 2B; here A reacts with B to form B and the original B, which acts as a catalyst is retained.
The graph of conversion of reactants to products with time is sigmoidal. The conversion is slow initially due to the absence of catalyst and then increases at a steady rate as products are formed, which also act as a catalyst. The rate of reaction again slows down with depletion of reactants.
Autocatalytic Reaction Examples
There are many chemical and biochemical reactions, which are autocatalytic. Some examples are:
- The reaction of oxalic acid with permanganate, here the Mn2+ ions are products and also act as a catalyst. The reaction is very slow at the start and speeds up with time as more and more products are formed.
2MnO4－ + 6H+ + 5C2H2O4 → 2Mn2+ + 8H2O + 10CO2
- Haloform reaction.
- Decomposition of Arsine is catalysed by Arsenic, which is produced in the reaction.
2AsH3 → 2As + 3H2
- Cooperative binding of haemoglobin with oxygen. Binding of one molecule of oxygen with haemoglobin increases the affinity of binding of more oxygen molecules to haemoglobin.
This was in brief about Autocatalytic Reaction. Get access to all the NEET questions with explanations, only at BYJU’S.