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. (a) Sketch the energy profile for the reaction, and label Ea and ΔE.

Key Concepts

Energy Profile Diagrams

Energy profile diagrams visually represent the energy changes during a chemical reaction. They plot the energy of the system against the progress of the reaction, showing the energy of reactants, products, and the activation energy (Ea). The diagram helps illustrate whether a reaction is exothermic or endothermic, as well as the energy barrier that must be overcome for the reaction to proceed.

Activation Energy (Ea)

Activation energy is the minimum energy required for reactants to undergo a chemical reaction. It represents the energy barrier that must be overcome for the reaction to proceed. In the given reaction, the activation energy is 7 kJ, indicating that this amount of energy must be supplied to initiate the reaction, regardless of whether the overall reaction is exothermic or endothermic.

Enthalpy Change (ΔE)

The enthalpy change (ΔE) of a reaction indicates the difference in energy between the reactants and products. A negative ΔE, such as -66 kJ in this case, signifies that the reaction releases energy to the surroundings, classifying it as exothermic. This value is crucial for understanding the thermodynamics of the reaction and its favorability under standard conditions.