Propene reacts with bromine to form C3H6Br2\mathrm{C_{3}H_{6}Br_{2}}C3H6Br2.
C3H6+Br2→C3H6Br2 \mathrm{C_{3}H_{6} + Br_{2} \rightarrow C_{3}H_{6}Br_{2}} C3H6+Br2→C3H6Br2The table shows the bonds in each molecule.
| Molecule | Bonds in one molecule |
|---|---|
| C3H6\mathrm{C_{3}H_{6}}C3H6 | six C−H\mathrm{C{-}H}C−H, one C−C\mathrm{C{-}C}C−C and one C=C\mathrm{C{=}C}C=C |
| Br2\mathrm{Br_{2}}Br2 | one Br−Br\mathrm{Br{-}Br}Br−Br |
| C3H6Br2\mathrm{C_{3}H_{6}Br_{2}}C3H6Br2 | six C−H\mathrm{C{-}H}C−H, two C−C\mathrm{C{-}C}C−C and two C−Br\mathrm{C{-}Br}C−Br |
| Bond | C−H\mathrm{C{-}H}C−H | C−C\mathrm{C{-}C}C−C | C=C\mathrm{C{=}C}C=C | Br−Br\mathrm{Br{-}Br}Br−Br | C−Br\mathrm{C{-}Br}C−Br |
|---|---|---|---|---|---|
| Bond energy (kJ/mol\mathrm{kJ/mol}kJ/mol) | 413 | 347 | 612 | 193 | 276 |
What is the energy change for the reaction?
−287 kJ/mol-287\,\mathrm{kJ/mol}−287kJ/mol
−94 kJ/mol-94\,\mathrm{kJ/mol}−94kJ/mol
+182 kJ/mol+182\,\mathrm{kJ/mol}+182kJ/mol
+94 kJ/mol+94\,\mathrm{kJ/mol}+94kJ/mol
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.