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1. Write oxidation and reduction half-equations and an overall equation to represent thernreaction occurring in the PEM fuel cell. Calculate the EMF produced under standardrnconditions. (4 marks)rnthe PEM is also often called a ‘proton-exchange membrane’ because one of its mainrnfunctions is to conduct protons from one half-cell to another.
Accepted Answer
1. Oxidation half-equation:
H2 → 2H+ + 2e-
Reduction half-equation:
O2 + 4H+ + 4e- → 2H2O
Overall equation:
2H2 + O2 → 2H2O
2. EMF calculation under standard conditions:
The EMF of a fuel cell can be calculated using the Nernst equation:
EMF = EMF° - (RT/nF) ln(Q)
where:
- EMF is the cell potential in volts
- EMF° is the standard cell potential in volts
- R is the ideal gas constant (8.314 J/mol·K)
- T is the temperature in Kelvin
- n is the number of moles of electrons transferred in the overall reaction
- Q is the reaction quotient
Under standard conditions (298 K, 1 atm), the EMF° of the PEM fuel cell is 1.23 V. The reaction quotient is 1 because the reactants and products are at their standard concentrations. Therefore, the EMF under standard conditions is:
EMF = 1.23 V - (8.314 J/mol·K / (4 mol·96485 C/mol)) ln(1)
EMF = 1.23 V
Therefore, the EMF produced by the PEM fuel cell under standard conditions is 1.23 V.
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