AQA GCSE Chemistry (8462), Higher tier · Energy changes › Chemical cells and fuel cells
Practise Fuel cells. 11 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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Name the only product of the reaction in a hydrogen fuel cell.
Water
Complete the half equation for the reaction at the negative electrode. H2 → 2H+ + ........
H2 → 2H+ + 2e−
Write the half equation for the reaction at the negative electrode.
CH3OH + H2O → CO2 + 6H+ + 6e−
State one similarity between a hydrogen fuel cell and a rechargeable battery.
Both convert chemical energy into electrical energy using a chemical reaction.
Complete the half equation for the reaction at the negative electrode. H2 + 2OH− → 2H2O + ........
H2 + 2OH− → 2H2O + 2e−
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
Hydrogen fuel cells can be used to power vehicles.
(a) Which two substances are supplied to a hydrogen fuel cell? Tick (✓) two boxes.[2]
Carbon dioxide
Hydrogen
Nitrogen
Oxygen or air
Water
(b) Name the only product of the reaction in a hydrogen fuel cell.[1]
(c) Is hydrogen oxidised or reduced in the fuel cell?[1]
(d) Give one advantage of a vehicle powered by a hydrogen fuel cell compared with a vehicle powered by a petrol engine.[1]
Show the answer and mark scheme
(a)Answer: Hydrogen; Oxygen or air
(b)Answer: Water
water
(c)Answer: Oxidised
oxidised
(d)Answer: No carbon dioxide is produced when it is used.
no carbon dioxide is produced (while it is being used) / only water is produced / no pollutants such as carbon monoxide are produced
Question 2Medium5 marks
The hydrogen fuel cell in a small drone produces 0.360 g of water each minute. 2H2 + O2 → 2H2O Relative formula mass (Mr): H2O = 18 The volume of one mole of any gas at room temperature and pressure is 24 dm3.
(a) Calculate the volume of hydrogen, at room temperature and pressure, used by the fuel cell each minute.[3]
(b) Calculate the volume of oxygen, at room temperature and pressure, used by the fuel cell each minute.[1]
(c) The fuel cell takes the oxygen it needs from the air. Suggest one advantage of this for a drone.[1]
Show the answer and mark scheme
(a)Answer: 0.480 dm3
0.360 ÷ 18 = 0.0200 (mol of water)
0.0200 mol of hydrogen reacts (1 : 1 ratio)
0.0200 × 24 = 0.480 (dm3)
(b)Answer: 0.240 dm3
0.0100 × 24 = 0.240 (dm3) (half the volume of hydrogen)
(c)Answer: The drone does not have to carry a tank of oxygen, so it is lighter.
the drone does not need to carry (a tank of) oxygen, so it is lighter / has more space
Question 3Hard6 marks
In a hydrogen fuel cell with an acid electrolyte:
hydrogen molecules lose electrons at the negative electrode to form hydrogen ions
oxygen molecules gain electrons at the positive electrode and react with hydrogen ions to form water.
(a) Complete the half equation for the reaction at the negative electrode. H2 → 2H+ + ........[1]
(b) Write the half equation for the reaction at the positive electrode.[2]
(c) Show how the two half equations combine to give the overall equation for the reaction in the fuel cell.[2]
(d) Explain whether hydrogen is oxidised or reduced in the fuel cell.[1]
Show the answer and mark scheme
(a)Answer: H2 → 2H+ + 2e−
2e−
(b)Answer: O2 + 4H+ + 4e− → 2H2O
correct species: O2 + H+ + e− → H2O
balanced: O2 + 4H+ + 4e− → 2H2O
(c)Answer: Double the negative electrode equation (2H2 → 4H+ + 4e−), add it to the positive electrode equation and cancel the hydrogen ions and electrons: 2H2 + O2 → 2H2O
multiply the negative electrode half equation by 2: 2H2 → 4H+ + 4e−
add the two half equations and cancel the H+ ions and electrons to give 2H2 + O2 → 2H2O