Substance that hasten chemical reaction time without themselves undergoing change are called

catalyst

Explanation:

A catalyst is a substance which increases or hastens the rate of a chemical reaction by taking the reaction through a different path which involves lower activation energy and thus more molecules can cross the energy barrier and convert to products.

Activation energy is the extra energy that must be supplied to reactants in order to cross the energy barrier and thus convert to products.

The catalyst itself does not take part in the chemical reaction and is regenerated as such at the end without undergoing any change.