1. When a catalyst is missing from a chemical reaction, what happens to the reaction?

The rate of the reaction slows down.

Explanation:

A catalyst speeds up a chemical reaction by decreasing its activation energy. Reactants have a range of energies, and only those with energies above the activation energy of the reaction are able to undergo the reaction. By lowering the activation energy, more reactants will have energies above it, enabling them to undergo the reaction.