Ethane reacts with bromine to form bromoethane and hydrogen bromide.
C2H6+Br2→C2H5Br+HBr \mathrm{C_2H_6 + Br_2 \rightarrow C_2H_5Br + HBr} C2H6+Br2→C2H5Br+HBrThe first table shows the number of each type of bond in one molecule.
| Substance | 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 |
|---|---|---|---|---|---|
| Ethane | 1 | 6 | 0 | 0 | 0 |
| Bromine | 0 | 0 | 1 | 0 | 0 |
| Bromoethane | 1 | 5 | 0 | 1 | 0 |
| Hydrogen bromide | 0 | 0 | 0 | 0 | 1 |
| 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) | 348 | 413 | 193 | 276 | 366 |
Calculate the energy change, in kJ/mol\mathrm{kJ/mol}kJ/mol, for the reaction.
Explain what happens to the temperature of the surroundings when this reaction takes place.
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.