Why do catalysts not alter the amounts of reactants and products present at equilibrium?

Verified step by step guidance

1. Understand the role of a catalyst: A catalyst is a substance that increases the rate of a chemical reaction by lowering the activation energy required for the reaction to proceed. It does this without being consumed in the reaction.
2. Recognize the principle of equilibrium: At equilibrium, the forward and reverse reaction rates are equal, and the concentrations of reactants and products remain constant. This state is determined by the equilibrium constant (K), which depends only on the temperature and not on the reaction pathway.
3. Explain how a catalyst affects reaction rates: A catalyst speeds up both the forward and reverse reactions equally by providing an alternative pathway with a lower activation energy. This means the system reaches equilibrium faster, but the relative rates of the forward and reverse reactions at equilibrium remain unchanged.
4. Clarify why the equilibrium constant (K) is unaffected: Since the catalyst does not change the energy levels of the reactants or products, it does not alter the thermodynamic properties of the reaction, such as the Gibbs free energy. Therefore, the equilibrium constant, which is derived from these properties, remains the same.
5. Conclude that the amounts of reactants and products at equilibrium are unchanged: Because the equilibrium constant (K) is not affected by the presence of a catalyst, the ratio of reactants to products at equilibrium remains constant, and the catalyst does not alter the equilibrium concentrations.

Key Concepts

Chemical Equilibrium

Chemical equilibrium occurs when the rates of the forward and reverse reactions in a chemical process are equal, resulting in constant concentrations of reactants and products. At this state, the system is dynamic, meaning that reactions continue to occur, but there is no net change in the amounts of substances involved.

Catalysts

Catalysts are substances that increase the rate of a chemical reaction without being consumed in the process. They work by lowering the activation energy required for the reaction to occur, allowing both the forward and reverse reactions to proceed more quickly, but they do not affect the position of the equilibrium.

Le Chatelier's Principle

Le Chatelier's Principle states that if a system at equilibrium is subjected to a change in concentration, temperature, or pressure, the system will adjust to counteract that change and restore a new equilibrium. However, since catalysts do not change the energy levels of reactants or products, they do not shift the equilibrium position.