Pent-1-ene reacts with hydrogen to form pentane.
CH2=CH−CH2−CH2−CH3+H2→CH3−CH2−CH2−CH2−CH3\mathrm{CH_{2}=CH-CH_{2}-CH_{2}-CH_{3} + H_{2} \rightarrow CH_{3}-CH_{2}-CH_{2}-CH_{2}-CH_{3}}CH2=CH−CH2−CH2−CH3+H2→CH3−CH2−CH2−CH2−CH3
| Bond | C=C\mathrm{C=C}C=C | C−C\mathrm{C-C}C−C | C−H\mathrm{C-H}C−H | H−H\mathrm{H-H}H−H |
|---|---|---|---|---|
| Bond energy / kJ mol−1\mathrm{kJ\,mol^{-1}}kJmol−1 | 612 | 347 | 413 | 436 |
What is the energy change for this reaction?
−125 kJ mol−1-125\,\mathrm{kJ\,mol^{-1}}−125kJmol−1
+125 kJ mol−1+125\,\mathrm{kJ\,mol^{-1}}+125kJmol−1
−561 kJ mol−1-561\,\mathrm{kJ\,mol^{-1}}−561kJmol−1
+222 kJ mol−1+222\,\mathrm{kJ\,mol^{-1}}+222kJmol−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.