Use bond energies: H−H=436\mathrm{H-H}=436H−H=436, Cl−Cl=243\mathrm{Cl-Cl}=243Cl−Cl=243, H−Cl=431 kJ mol−1\mathrm{H-Cl}=431\,\mathrm{kJ\,mol^{-1}}H−Cl=431kJmol−1. For H2+Cl2→2HCl\mathrm{H_2+Cl_2\rightarrow2HCl}H2+Cl2→2HCl, what is the energy change?
−183 kJ mol−1-183\,\mathrm{kJ\,mol^{-1}}−183kJmol−1
+183 kJ mol−1+183\,\mathrm{kJ\,mol^{-1}}+183kJmol−1
−614 kJ mol−1-614\,\mathrm{kJ\,mol^{-1}}−614kJmol−1
+862 kJ mol−1+862\,\mathrm{kJ\,mol^{-1}}+862kJmol−1
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.