Edexcel Jun 2011 Paper 5 Q15 (with explained solutions) |

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Edexcel Jun 2011 Paper 5 Q15

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15 Hydrogen gas can be used as a fuel in car engines by being burnt in a combustion reaction or reacted with oxygen in a fuel cell to produce electricity. (a) Write half-equations for the reaction of hydrogen gas at the anode and oxygen gas at the cathode in the fuel cell. Anode Cathode (b) Describe one advantage of using hydrogen in fuel cells rather than burning the hydrogen directly. PMT (2) (1)(c) Other fuels, such as ethanol, can also be used in fuel cells. By considering the possible sources of ethanol and hydrogen, explain why some scientists believe the use of such cells could provide a more sustainable source of energy for cars, compared with fossil fuels. (3)(Total for Question 15 = 6 marks) 16 *P38480A01624*<br />

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Reject Mark Acceptable Answers2H2O (1) Either Anode H22e(-)2H+ (1) Cathode O2 + 4H+ + 4e(-) Or Anode H2 + 2OH-2e(-)2H2O (1) Cathode O2 + 2H2O + 4e(-) Electrons can be on either side of the equation Allow multiples Allow equilibria signs Ignore state symbols4OH- (1) Reject Just easier to control Reject Mark Mark Acceptable Answers One advantage e.g. quieter, more efficient (energy transfer), no NOx formed Ignore references to carbon dioxide and / or water as only product Acceptable Answers Ethanol can be obtained from biomass / plants / fermentation / ethanol is a bio fuel (1) hydrogen from (electrolysis of) water using a non-fossil source of energy (1) these are renewable / fossil fuels are a finite resource (1) Allow for third mark so less burning/use of fossil fuels hence lower carbon emissions / less impact on greenhouse effect Question Number 15 (a) Question Number 15 (b) Question Number 15 (c)<br />

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