Camping stoves burn propane gas.
C3H8(g)+5O2(g)→3CO2(g)+4H2O(g)\mathrm{C_{3}H_{8}(g)} + \mathrm{5O_{2}(g)} \rightarrow \mathrm{3CO_{2}(g)} + \mathrm{4H_{2}O(g)}C3H8(g)+5O2(g)→3CO2(g)+4H2O(g)
A propane molecule contains two C–C bonds and eight C–H bonds. Each carbon dioxide molecule contains two C=O bonds and each water molecule contains two O–H bonds.
The table shows some bond energies.
| Bond | Bond energy / kJ mol−1\mathrm{kJ\,mol^{-1}}kJmol−1 |
|---|---|
| C–C | 347 |
| C–H | 413 |
| O=O | 498 |
| C=O | 805 |
| O–H | 464 |
Calculate the energy change when one mole of propane burns completely.
Calculate the heat energy released when 110 g of propane burns completely. Relative formula mass: C3H8=44\mathrm{C_{3}H_{8}} = 44C3H8=44
A data book gives the energy change for the complete combustion of propane as −2220kJ mol−1-2220 \mathrm{kJ\,mol^{-1}}−2220kJmol−1. This value is for water formed as a liquid.
Suggest two reasons why your answer to (a) is different from the data book value.
A student says, "Burning one mole of butane, C4H10\mathrm{C_{4}H_{10}}C4H10, will release less energy than burning one mole of propane, because butane has more bonds to break."
Explain why the student is wrong.
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.