Question

How do the following help in bringing about a chemical change?

catalyst .

Answer 1

A catalyst can either increases or decreases the rate of chemical reaction and some chemical reactions need a catalyst to change the rate of the reaction, in case it is too slow or too fast 

1. Positive catalyst: When a catalyst increase the rate of reaction finely divided iron is used as a positive catalyst in the manufacturing of ammonia from hydrogen and nitrogen.

\[\ce{N2 + 3H2 ⇌[Iron (Catalyst) 200-900][450°C] 2NH3 + Heat}\]

2. Negative Catalyst: When a catalyst decreases the rate of reaction.
Ex. Phosphoric acid act as a negative catalyst to decrease the rate of the decomposition of hydrogen peroxide.