If a catalyst changes the activation energy of a forward reaction from 28.0 kcal/mol to 23.0 kcal/mol, what effect does it have on the reverse reaction?

Verified step by step guidance

1. Understand the role of a catalyst: A catalyst lowers the activation energy of a reaction by providing an alternative pathway for the reaction to occur. This effect applies to both the forward and reverse reactions equally.
2. Recognize that the activation energy for the reverse reaction is related to the forward reaction's activation energy and the enthalpy change (ΔH) of the reaction. The relationship can be expressed as: $E{a}_{\mathrm{reverse}}=E{a}_{\mathrm{forward}}+\; \Delta H$ (if the forward reaction is exothermic, ΔH is negative).
3. When a catalyst lowers the activation energy of the forward reaction, it also lowers the activation energy of the reverse reaction by the same amount. In this case, the forward reaction's activation energy decreases by $28.0\; -\; 23.0\; =\; 5.0$ kcal/mol.
4. Apply the same reduction to the reverse reaction's activation energy. If the original activation energy for the reverse reaction is known, subtract 5.0 kcal/mol from it to find the new activation energy for the reverse reaction.
5. Conclude that the catalyst affects both the forward and reverse reactions equally, lowering their activation energies by the same amount, which increases the rate of both reactions without altering the equilibrium position.

Key Concepts

Activation Energy

Activation energy is the minimum energy required for a chemical reaction to occur. It represents the energy barrier that reactants must overcome to transform into products. A lower activation energy means that more molecules have sufficient energy to react, thus increasing the reaction rate.

Catalysts

Catalysts are substances that increase the rate of a chemical reaction without being consumed in the process. They work by providing an alternative reaction pathway with a lower activation energy. Importantly, catalysts affect both the forward and reverse reactions equally, thereby influencing the overall reaction dynamics.

Equilibrium and Reaction Rates

In a reversible reaction, the rates of the forward and reverse reactions determine the position of equilibrium. When a catalyst lowers the activation energy for the forward reaction, it also lowers it for the reverse reaction. This means that the catalyst accelerates both directions, allowing the system to reach equilibrium faster without altering the equilibrium position.