Question

What is wrong about a positive catalyst?
A. It lowers the energy of activation of forward reaction.
B. It lowers the threshold energy level.
C. It lowers the energy of activation of backward reaction.
D. It makes the reaction more exothermic and endothermic.

Answer 1

A positive catalyst is a substance which increases the rate of reaction without reacting. This action is done by decreasing the activation energy and following the smaller path.

Complete step by step answer:
In a reaction, if a substance is used in order to alter the rate of reaction then that substance is called catalyst. And this process of adding a substance which alters the rate of reaction is called catalysis.
There are two types of catalysts:
1. Positive catalyst
2. Negative catalyst
Positive catalyst is the substance which increases the rate of reaction without getting consumed in reaction. This increase in rate of reaction is done by decreasing the rate of reaction by following the smaller path.
Positive catalyst lowers the energy of activation of forward reaction.
Positive catalyst lowers the threshold energy level.
Positive catalyst lowers the energy of activation of backward reaction.
But it does not make the reaction more exothermic and endothermic.
Hence, this statement is wrong about positive catalysts.

So, the correct answer is Option D.

Note: Negative catalyst decreases the rate of if added to the reaction. It also does not get consumed in the reaction. Negative catalyst decreases the rate of reaction and that’s why it is called an inhibitor. The inhibitor can produce this effect by selectively poisoning only certain types of active sites. Another mechanism is the modification of surface geometry. For instance, in hydrogenation operations, large planes of metal surface function as sites of hydrogenolysis catalysts while sites catalyzing hydrogenation of unsaturated are smaller.