Ethene reacts with bromine to form 1,2-dibromoethane.
The equation shows the structural formulas of the reactants and products involved in this reaction:
HH\/C=C/\HH+Br−Br→HH∣∣H−C−C−H∣∣BrBr \begin{array}{c} \text{H} \quad \text{H} \\ \backslash \quad / \\ \text{C}=\text{C} \\ / \quad \backslash \\ \text{H} \quad \text{H} \end{array} + \quad \text{Br}-\text{Br} \quad \rightarrow \quad \begin{array}{c} \text{H} \quad \text{H} \\ | | \\ \text{H}-\text{C}-\text{C}-\text{H} \\ | | \\ \text{Br} \quad \text{Br} \end{array} HH\/C=C/\HH+Br−Br→HH∣∣H−C−C−H∣∣BrBrUse the bond energy data in the table below to calculate the energy change, in kJ mol−1\text{kJ mol}^{-1}kJ mol−1, for this reaction.
| Bond | Bond energy in kJ mol−1\text{kJ mol}^{-1}kJ mol−1 |
|---|---|
| C=C | 614 |
| C—H | 413 |
| Br—Br | 193 |
| C—C | 348 |
| C—Br | 276 |
94 exam-style questions on Edexcel GCSE Chemistry 8.2 Heat energy changes in chemical reactions, covering 8.2.1 Exothermic and endothermic changes, 8.2.2 Bond breaking, bond making and overall energy change, 8.2.3 Calculating energy change from bond energies, and 8.2.4 Activation energy and reaction profiles. Each one has a worked solution and a mark scheme showing where the marks go.