Question

Consider the following reaction mechanism and its associated energy diagram:

S1: C₂H4 (g) + HBr(g) --> C₂H5+ + Br
S2:
C₂H5 + Br --> C₂H5Br (1)

Answer 1

From the energy diagram, we can see that the reaction mechanism is an example of a two-step reaction. The first step (S1) involves the combination of ethylene (C₂H4) and hydrogen bromide (HBr) to form an ethyl cation (C₂H5+) and a bromide anion (Br). In the second step (S2), the ethyl cation and bromide anion combine to form ethyl bromide (C₂H5Br). The reaction is exergonic as evidenced by the fact that the activation energy, represented by the peak in the energy diagram, is negative. This indicates that the reaction releases energy.