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A fuel cell operates with methanol as the fuel and oxygen as the oxidant. The overall reaction is CH3OH(l) + 3/2 O2(g) → CO2(g) + 2H2O(l) At 298 K, the standard Gibbs energies of formation of CH3OH(l), H2O(l), and CO2(g) are −166.2, −237.2, and −394.4 kJ mol−1, respectively. If the standard enthalpy of combustion of methanol is −726 kJ mol−1, what is the efficiency of the fuel cell?
- 87%
- 90%
- 97%
- 80%
Correct answer: 90%
Solution
The efficiency of the fuel cell is calculated by comparing the useful electrical energy output to the energy input from the fuel. Given the standard Gibbs free energy change for the reaction and the enthalpy of combustion, the efficiency can be determined to be 90%, indicating that a significant portion of the energy from methanol is converted into electrical energy.
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