The gas-phase reaction Cl(g) + HBr(g) → HCl(g) + Br(g) has an overall energy change of -66 kJ. The activation energy for the reaction is 7 kJ. (b) What is the activation energy for the reverse reaction?

Verified step by step guidance

1. Identify the given values: the overall energy change (\(\Delta H\)) for the forward reaction is -66 kJ, and the activation energy (\(E_a\)) for the forward reaction is 7 kJ.
2. Understand that the activation energy for the reverse reaction can be calculated using the relationship: \(E_a^{reverse} = E_a^{forward} + \Delta H\).
3. Substitute the given values into the equation: \(E_a^{reverse} = 7 \text{ kJ} - 66 \text{ kJ}\).
4. Calculate the sum to find the activation energy for the reverse reaction.
5. Interpret the result: if the activation energy for the reverse reaction is positive, it indicates that energy is required to initiate the reverse reaction; if negative, it suggests an unusual scenario in chemical kinetics.

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. In this context, the activation energy for the forward reaction is given as 7 kJ, indicating the energy needed to initiate the reaction between Cl(g) and HBr(g).

Enthalpy Change

The enthalpy change (ΔH) of a reaction is the difference in energy between the products and reactants. A negative ΔH, such as -66 kJ in this reaction, indicates that the reaction is exothermic, meaning it releases energy. This value is crucial for determining the activation energy of the reverse reaction, as it affects the energy landscape of the reaction pathway.

Reverse Reaction Activation Energy

The activation energy for the reverse reaction can be calculated by adding the enthalpy change to the activation energy of the forward reaction. In this case, the activation energy for the reverse reaction is the sum of the activation energy of the forward reaction (7 kJ) and the absolute value of the enthalpy change (-66 kJ), resulting in a higher energy barrier for the reverse process.