NCEA Level 2 Organic Chemistry Practice Exam

A catalyst is a substance that is added to a chemical reaction to increase the rate at which the reaction occurs. It accomplishes this by providing an alternative reaction pathway with a lower activation energy, which allows more molecules to react successfully at a given temperature. Importantly, a catalyst is not consumed in the reaction; it remains unchanged after the reaction has taken place and can be used again in subsequent reactions.

The fact that a catalyst speeds up the reaction rate while remaining unchanged is what distinguishes it from other substances involved in chemical reactions. This ability to enhance the reaction kinetics without being altered in the process makes catalysts essential in both industrial applications and biological systems, such as enzymes in metabolic pathways.

The other choices misrepresent the nature of catalysts. Catalysts do not slow down the reaction rate nor are they consumed in the reaction, which eliminates those possibilities. Additionally, while a catalyst may influence the pathway of the reaction, it does not inherently change the products formed; those depend on the initial reactants and the conditions of the reaction. Thus, the correct understanding is that a catalyst speeds up the reaction rate without undergoing any permanent changes itself.