How is a chemical reaction affected by the addition of a catalyst?
Rate of reaction can be increased by using a catalyst. A catalyst lowers the activation energy, for example, by providing a surface for the reaction to occur on. A catalyst participates in a reaction is not used up in a reaction itself.
Enzymes are protein molecules which serve as catalysts for chemical reactions.
A catalyst is a substance which will decrease the activation energy for a reaction.
So why is this important? Enzymes will make reactions occur much more easily, quickly and more efficiently than they ever would without the enzyme.
Here is a video of an enzyme demonstration I like to share with my students. The video shows how an enzyme present in our saliva (spit) can aid in the process of digestion by acting on starches present in the foods we eat.
Video from: Noel Pauller
Hope this was helpful!