The Sabatier reaction is utilized on the International Space Station to recover water by reacting carbon dioxide from the cabin air with waste hydrogen gas:
CO2(g)+4H2(g)→CH4(g)+2H2O(g) \text{CO}_2\text{(g)} + 4\text{H}_2\text{(g)} \rightarrow \text{CH}_4\text{(g)} + 2\text{H}_2\text{O(g)} CO2(g)+4H2(g)→CH4(g)+2H2O(g)Mean bond enthalpies are shown in the table below:
| Bond | Mean bond enthalpy / kJ mol−1\text{kJ mol}^{-1}kJ mol−1 |
|---|---|
| C-H\text{C-H}C-H | 413 |
| C=O\text{C=O}C=O | 805 |
| H-H\text{H-H}H-H | 436 |
| O-H\text{O-H}O-H | 463 |
What is the enthalpy change, in kJ mol−1\text{kJ mol}^{-1}kJ mol−1, for this reaction?
−150-150−150
+150+150+150
−776-776−776
−955-955−955
31 exam-style questions on OCR A A Level Chemistry Enthalpy changes. Each one has a worked solution and a mark scheme showing where the marks go.