What is the term for a substance that decreases the activation energy of a chemical reaction?

A substance that decreases the activation energy of a chemical reaction is referred to as a catalyst. Catalysts work by providing an alternative pathway for the reaction that requires less energy to occur, thereby speeding up the reaction without being consumed in the process. This ability to lower activation energy is crucial in many biological and chemical processes, as it allows reactions to occur more readily under standard conditions.

In contrast, inhibitors are substances that slow down or prevent a chemical reaction, and reactants are the starting materials in a chemical reaction that undergo transformation. Solvents are substances that dissolve other substances but do not directly participate in the chemical reaction in the same way as catalysts do. Therefore, the role of a catalyst is uniquely significant in enhancing the rate of reactions by lowering the energy barrier, which is why it is the correct choice in this case.