Ethene reacts with bromine at room temperature to form a single product, CH2BrCH2Br\mathrm{CH_{2}BrCH_{2}Br}CH2BrCH2Br.
C2H4(g)+Br2(l)→CH2BrCH2Br(l)\mathrm{C_{2}H_{4}(g)} + \mathrm{Br_{2}(l)} \rightarrow \mathrm{CH_{2}BrCH_{2}Br(l)}C2H4(g)+Br2(l)→CH2BrCH2Br(l)
The table shows some bond energies.
| Bond | C=C | C–C | C–H | Br–Br | C–Br |
|---|---|---|---|---|---|
| Bond energy / kJ mol−1\mathrm{kJ\,mol^{-1}}kJmol−1 | 612 | 348 | 413 | 193 | 276 |
Explain why this reaction is described as an addition reaction.
Calculate the energy change for the reaction of one mole of ethene with bromine.
State whether the reaction is exothermic or endothermic. Explain your answer using your result from (b).
Propene, CH2=CHCH3\mathrm{CH_{2}=CHCH_{3}}CH2=CHCH3, also reacts with bromine to form CH2BrCHBrCH3\mathrm{CH_{2}BrCHBrCH_{3}}CH2BrCHBrCH3.
Without doing a full calculation, predict the energy change for the reaction of one mole of propene with bromine. Justify your answer.
A student says: "Bromine water can tell ethene and propene apart." Evaluate this statement.
36 exam-style questions on Edexcel GCSE Chemistry 10.2 Hydrocarbons, covering 10.2.1 Formulae and structures of the alkanes, 10.2.2 Alkenes and the C=C functional group, 10.2.3 Addition reactions of alkenes and testing for unsaturation, and 10.2.4 Combustion of alkanes and alkenes. Each one has a worked solution and a mark scheme showing where the marks go.