Hydrogen reacts with chlorine to make hydrogen chloride.
H2+Cl2→2HCl \mathrm{H_{2} + Cl_{2} \rightarrow 2HCl} H2+Cl2→2HClThe table shows some bond energies.
| Bond | H−H\mathrm{H{-}H}H−H | Cl−Cl\mathrm{Cl{-}Cl}Cl−Cl | H−Cl\mathrm{H{-}Cl}H−Cl |
|---|---|---|---|
| Bond energy (kJ/mol\mathrm{kJ/mol}kJ/mol) | 436 | 243 | 432 |
What is the energy change for the reaction?
+185 kJ/mol+185\,\mathrm{kJ/mol}+185kJ/mol
+247 kJ/mol+247\,\mathrm{kJ/mol}+247kJ/mol
+1543 kJ/mol+1543\,\mathrm{kJ/mol}+1543kJ/mol
−185 kJ/mol-185\,\mathrm{kJ/mol}−185kJ/mol
51 exam-style questions on OCR GCSE Chemistry 3.2 Energetics, covering 3.2.1 Exothermic and endothermic reactions and reaction profiles and 3.2.2 Calculating energy change from bond energies. Each one has a worked solution and a mark scheme showing where the marks go.