The average bond energies of some covalent bonds are shown in the table below.
Nitrogen gas reacts with hydrogen gas to produce ammonia gas according to the following equation:
N2(g)+3H2(g)→2NH3(g) \text{N}_2(\text{g}) + 3\text{H}_2(\text{g}) \rightarrow 2\text{NH}_3(\text{g}) N2(g)+3H2(g)→2NH3(g)| Bond | Bond energy in kJ mol−1\text{kJ mol}^{-1}kJ mol−1 |
|---|---|
| N≡N\text{N}\equiv\text{N}N≡N | 945 |
| H—H\text{H}—\text{H}H—H | 436 |
| N—H\text{N}—\text{H}N—H | 391 |
Calculate the overall energy change, in kJ mol−1\text{kJ mol}^{-1}kJ mol−1, for the reaction of 1 mol of nitrogen gas, N2\text{N}_2N2, with 3 mol of hydrogen gas, H2\text{H}_2H2, to form 2 mol of ammonia gas, NH3\text{NH}_3NH3.
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.