Iodine reacts with chlorine to make iodine monochloride.
Reaction 1:
I−I+Cl−Cl→2I−Cl \mathrm{I-I + Cl-Cl \rightarrow 2I-Cl} I−I+Cl−Cl→2I−ClThe table shows average bond energies.
| Bond | Average bond energy (kJ/mol) |
|---|---|
| I−I\mathrm{I-I}I−I | 151 |
| Cl−Cl\mathrm{Cl-Cl}Cl−Cl | 243 |
| I−Cl\mathrm{I-Cl}I−Cl | 208 |
A reaction profile for Reaction 1 gives these energy values.
| Point on the reaction profile | Energy (kJ/mol) |
|---|---|
| Reactants | +35 |
| Highest point | +160 |
| Products | +10 |
Iodine monochloride can decompose in the reverse reaction.
Reaction 2:
2I−Cl→I−I+Cl−Cl \mathrm{2I-Cl \rightarrow I-I + Cl-Cl} 2I−Cl→I−I+Cl−ClReaction 2 follows the same reaction pathway as Reaction 1, but in the opposite direction.
Calculate the energy change for Reaction 1 using the average bond energies.
Energy change = .................... kJ/mol
Compare the value calculated in (a) with the overall energy change shown by the reaction profile data.
Explain why the values may be slightly different.
A student sketches the reaction profile for Reaction 2. On the sketch:
Explain how each arrow should be corrected. Give the correct value shown by each arrow.
Calculate the activation energy for Reaction 1.
Explain why the activation energy for Reaction 2 is larger than the activation energy for Reaction 1.
106 exam-style questions on OCR GCSE Chemistry 3.2 Energetics, covering 3.2.1 Exothermic and endothermic reactions and reaction profiles and 3.2.2 Calculating energy change from bond energies. Each one has a worked solution and a mark scheme showing where the marks go.