The following reactions were investigated at 298 K using the average bond energies…
CHEMISTRY · Single correct · A Level · Chemistry · Energetics · Energetics
Problem
The following reactions were investigated at 298 K using the average bond energies listed below.
Reaction 1: H₂(g) + Br₂(g) → 2 HBr(g)
Reaction 2: H₂(g) + Cl₂(g) → 2 HCl(g)
Average bond energies (kJ mol⁻¹): H–H 436, Br–Br 193, Cl–Cl 242, H–Br 368, H–Cl 431
The calculated enthalpy change for Reaction 2 is significantly more negative than that for Reaction 1. Which of the following best accounts for this difference?
(a) The Cl–Cl bond broken in Reaction 2 is much weaker than the Br–Br bond broken in Reaction 1, so less energy is absorbed in Reaction 2.
(b) Only the H–H bond needs to be broken in Reaction 2, whereas Reaction 1 must break both an H–H bond and a Br–Br bond, requiring more energy overall.
(c) The H–Cl bond formed in Reaction 2 is considerably stronger than the H–Br bond formed in Reaction 1.
(d) Reaction 1 forms twice as many product bonds as Reaction 2, so it releases more energy than Reaction 2.