What is the half-cell reactions in a hydrogen fuel cell, and calculate the standard voltage at 25°C
H2(g)+ O2(g)------>2H2O(l)
I think you made a typo. The reaction I think, is 2H2 + O2 ==> 2H2O
H2 ==> 2H^+ + 2e Eo = ??
O2 + 4H^+ + 4e Eo = +1.229
Eocell = ??
Thank you so much
In a hydrogen fuel cell, the half-cell reactions are the separate reactions that occur at the two electrodes of the cell. In this fuel cell, hydrogen and oxygen react to produce water. The reaction can be divided into two half-cell reactions:
1) At the anode (negative electrode):
H2(g) → 2H+(aq) + 2e−
2) At the cathode (positive electrode):
O2(g) + 4H+(aq) + 4e− → 2H2O(l)
The overall cell reaction is the combination of these two half-cell reactions, and it represents the complete process of hydrogen and oxygen being converted into water.
Now, to calculate the standard voltage at 25°C for the hydrogen fuel cell, we can use the Nernst equation. The Nernst equation relates the standard cell potential to the reaction quotient (Q) using the equation:
Ecell = E°cell - (RT/nF) * ln(Q)
Where:
- Ecell is the cell potential
- E°cell is the standard cell potential
- 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 balanced half-cell reactions
- F is the Faraday constant (96485 C/mol)
- ln is the natural logarithm
In our case, since both half-cell reactions involve the transfer of 2 moles of electrons, the value of n will be 2.
To calculate the standard voltage at 25°C, we need to know the standard reduction potentials of the half-cell reactions. The standard reduction potential of the hydrogen half-cell (H2 → 2H+) is 0 V, and the standard reduction potential of the oxygen half-cell (O2 + 4H+ + 4e− → 2H2O) is 1.23 V.
Using the Nernst equation, we can substitute the given values:
Ecell = E°cell - (RT/nF) * ln(Q)
Ecell = (1.23 V) - ((8.314 J/(mol·K)) * (298 K) / (2 * 96485 C/mol)) * ln(1)
Since ln(1) equals 0, the second term becomes 0, resulting in:
Ecell = 1.23 V
Therefore, the standard voltage at 25°C for the hydrogen fuel cell is 1.23 V.