Predict the standard cell potential and calculate the standard reaction Gibbs free energy for galvanic cells having the following cell reactions:
2H2+O2=2H2O in acidic solution
2H2+O2=2H2O in basic solution
I understand the idea behind the problem, but I am not sure how the acidity or basicity affects the problem. Thanks.
The E value differs for acid vs basic solution. Look in the reduction potential table for these two values.I don't remember them off hand but I think 0.82 sounds familiar.
To predict the standard cell potential and calculate the standard reaction Gibbs free energy for galvanic cells, you need to use the Nernst equation and the standard reduction potentials.
In general, the acidity or basicity of the solution can affect the reactions occurring at the electrodes. For a galvanic cell, the half-reactions at the anode and cathode are written differently depending on the acidity or basicity of the solution.
1. In acidic solution:
For the reaction 2H2 + O2 → 2H2O, we can split it into two half-reactions:
a) The anode half-reaction: 2H2O → O2 + 4H+ + 4e-
b) The cathode half-reaction: O2 + 4H+ + 4e- → 2H2O
The standard reduction potentials for these half-reactions can be found in tables, usually referenced to the standard hydrogen electrode (SHE) with a potential of 0 V.
- The standard reduction potential for the anode half-reaction is -1.23 V.
- The standard reduction potential for the cathode half-reaction is 1.23 V (opposite sign of anode).
To calculate the standard cell potential (E°cell), you subtract the reduction potential of the anode half-reaction from the reduction potential of the cathode half-reaction:
E°cell = E°cathode - E°anode
E°cell = (1.23 V) - (-1.23 V) = 2.46 V
To calculate the standard reaction Gibbs free energy (ΔG°), you can use the equation:
ΔG° = -nFE°cell
Where n is the number of moles of electrons transferred and F is the Faraday constant.
2. In basic solution:
In basic solution, you need to add OH- ions to balance the charges in the half-reactions.
For the reaction 2H2 + O2 → 2H2O, the half-reactions become:
a) The anode half-reaction: 4OH- → O2 + 2H2O + 4e-
b) The cathode half-reaction: O2 + 4H2O + 4e- → 4OH-
The standard reduction potentials for these half-reactions remain the same.
After obtaining the standard reduction potentials, you can follow the steps mentioned earlier to calculate the standard cell potential and the standard reaction Gibbs free energy for the galvanic cell in basic solution.
Remember to consider the correct half-reactions and adjust accordingly depending on whether the solution is acidic or basic.