The energy change for the reaction below is −92 kJ mol−1-92\,\mathrm{kJ\,mol^{-1}}−92kJmol−1.
N2+3H2→2NH3\mathrm{N_{2} + 3H_{2} \rightarrow 2NH_{3}}N2+3H2→2NH3
Bond energies: N≡N=945 kJ mol−1\mathrm{N\equiv N} = 945\,\mathrm{kJ\,mol^{-1}}N≡N=945kJmol−1 and H−H=436 kJ mol−1\mathrm{H-H} = 436\,\mathrm{kJ\,mol^{-1}}H−H=436kJmol−1.
What is the mean bond energy of the N−H\mathrm{N-H}N−H bond, to the nearest whole number?
246 kJ mol−1246\,\mathrm{kJ\,mol^{-1}}246kJmol−1
360 kJ mol−1360\,\mathrm{kJ\,mol^{-1}}360kJmol−1
391 kJ mol−1391\,\mathrm{kJ\,mol^{-1}}391kJmol−1
782 kJ mol−1782\,\mathrm{kJ\,mol^{-1}}782kJmol−1
53 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.