What role does a catalyst play in a chemical reaction?

A catalyst plays a crucial role in a chemical reaction by lowering the activation energy required for the reaction to occur. Activation energy is the minimum energy that reacting species must possess for a reaction to proceed. By reducing this energy barrier, catalysts enable reactions to occur more easily and at a faster rate, without being consumed or permanently altered by the reaction themselves.

This characteristic is essential for many biological and industrial processes, where catalysts can facilitate reactions under milder conditions that might not be feasible otherwise. Catalysts achieve this by providing an alternative reaction pathway that has a lower energy requirement.

Other options do not accurately reflect the function of a catalyst. Increasing activation energy is contrary to what a catalyst does, starting a reaction without altering reactants misrepresents the catalyst's function since it does not initiate reactions but rather speeds them up, and acting as a reactant suggests that the catalyst undergoes a permanent change or is consumed in the reaction, which is not the case.