Bromine converts ethane into bromoethane. Hydrogen bromide is also formed.
C2H6+Br2→C2H5Br+HBr \mathrm{C_{2}H_{6} + Br_{2} \rightarrow C_{2}H_{5}Br + HBr} C2H6+Br2→C2H5Br+HBrThe bonds in one molecule of each substance are shown in the table.
| Substance | Bonds in one molecule |
|---|---|
| C2H6\mathrm{C_{2}H_{6}}C2H6 | one C−C\mathrm{C{-}C}C−C bond and six C−H\mathrm{C{-}H}C−H bonds |
| Br2\mathrm{Br_{2}}Br2 | one Br−Br\mathrm{Br{-}Br}Br−Br bond |
| C2H5Br\mathrm{C_{2}H_{5}Br}C2H5Br | one C−C\mathrm{C{-}C}C−C bond, five C−H\mathrm{C{-}H}C−H bonds and one C−Br\mathrm{C{-}Br}C−Br bond |
| HBr\mathrm{HBr}HBr | one H−Br\mathrm{H{-}Br}H−Br bond |
| Bond | C−C\mathrm{C{-}C}C−C | C−H\mathrm{C{-}H}C−H | Br−Br\mathrm{Br{-}Br}Br−Br | C−Br\mathrm{C{-}Br}C−Br | H−Br\mathrm{H{-}Br}H−Br |
|---|---|---|---|---|---|
| Bond energy (kJ/mol\mathrm{kJ/mol}kJ/mol) | 347 | 413 | 193 | 276 | 366 |
What is the energy change when one mole of ethane reacts as shown?
+330 kJ/mol+330\,\mathrm{kJ/mol}+330kJ/mol
−36 kJ/mol-36\,\mathrm{kJ/mol}−36kJ/mol
−449 kJ/mol-449\,\mathrm{kJ/mol}−449kJ/mol
+36 kJ/mol+36\,\mathrm{kJ/mol}+36kJ/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.