Ethene reacts with hydrogen: C2H4+H2\text{C}_2\text{H}_4 + \text{H}_2C2H4+H2 goes to C2H6\text{C}_2\text{H}_6C2H6. The table gives the bond energies.
Table: The bond energies of the bonds in the reactants and in the product
| Bond | Bond energy in kJ/mol |
|---|---|
| C=C\text{C=C}C=C | 612 |
| C-C\text{C-C}C-C | 347 |
| C-H\text{C-H}C-H | 413 |
| H-H\text{H-H}H-H | 436 |
What is the overall energy change of the reaction?
−5525 kJ/mol-5525\ \text{kJ/mol}−5525 kJ/mol
+125 kJ/mol+125\ \text{kJ/mol}+125 kJ/mol
−125 kJ/mol-125\ \text{kJ/mol}−125 kJ/mol
+2825 kJ/mol+2825\ \text{kJ/mol}+2825 kJ/mol
39 exam-style questions on AQA GCSE Chemistry 5.1 Exothermic and endothermic reactions, covering 5.1.1 Energy transfer during exothermic and endothermic reactions, 5.1.2 Reaction profiles, and 5.1.3 The energy change of reactions. Each one has a worked solution and a mark scheme showing where the marks go.