Question

A __ is a substance which changes the rate of a chemical reaction without itself undergoing any chemical change.

Answer 1

A catalyst is a substance which changes the rate of a chemical reaction without itself undergoing any chemical change.Some reactions need a catalyst to speed up or slow down the reaction.

For example: Manganese dioxide acts as a catalyst for the decomposition of potassium chlorate into potassium chloride and oxygen at a lower temperature.Manganese dioxide does not undergo any change in its chemical composition.