Question

Which of the following statements is/are not correct?

• A. A catalyst always increases the speed of a reaction.
• B. A catalyst is always an external substance added to the reaction mixture.
• C. A catalyst does not take part in the reaction.
• D. A catalyst may affect the nature of the products formed.

Answer 1

Answer: (A), (B)

A catalyst is a substance that may increase or decrease the speed of reaction. It may be added from outside and sometimes may be produced during the reaction. Catalysts are not consumed, they are recycled. Often only tiny amounts are required. A catalyst does not take part in the reaction and it will not take part in the product.

The enzymes in saliva, for example, are catalysts in digestion. I

n chemistry, a substance that causes a chemical reaction to occur but is not itself involved in the reaction.
Hence, options $B$ and $D$ are correct options.