Question

The gas-phase reaction Cl(g)+HBr(g)−→−HCl(g)+Br(g) has an overall energy change of −66kJ. The activation energy for the reaction is 7 kJ. (a) Sketch the energy profile for the reaction, and label Ea and ΔE. (b) What is the activation energy for the reverse reaction?

Answer 1

73 kJ

Step-by-step explanation:

Let's refer to the attached energy profile.

The activation energy (Ea) is the energy that the reactants have to gain to reach the transition state, that is, the top of the energy curve. Ea = 7 kJ

The overall energy change (ΔE) is the difference in energy between the products and the reactants. When the energy of the products is lower than the energy of the reactants, ΔE < 0 and the reaction is exothermic. ΔE is -66 kJ

If we think about the activation energy for the reverse reaction, it would be the energy required for the reactants (products in the direct reaction) to reach the transition state. We can see in the drawing that it is equal to

Ea + |ΔE| = 7 kJ + 66 kJ = 73 kJ