A scientist models the reaction in a hydrogen fuel cell using these half equations:
H2(g)→2H+(aq)+2e−\text{H}_2\text{(g)} \rightarrow 2\text{H}^+\text{(aq)} + 2e^-H2(g)→2H+(aq)+2e−
O2(g)+4H+(aq)+4e−→2H2O(l)\text{O}_2\text{(g)} + 4\text{H}^+\text{(aq)} + 4e^- \rightarrow 2\text{H}_2\text{O(l)}O2(g)+4H+(aq)+4e−→2H2O(l)
The model represents 12 oxygen molecules reacting completely.
Calculate the number of hydrogen molecules that react and the number of water molecules that form.
Explain why electrons are not included in the overall equation.
90 exam-style questions on AQA GCSE Chemistry 5.2 Chemical cells and fuel cells, covering 5.2.1 Cells and batteries, 5.2.2a Fuel cells, and 5.2.2b Half equations for hydrogen fuel cells. Each one has a worked solution and a mark scheme showing where the marks go.