The cell potential for the following electrochemical system at 25°...
Solution:
The cell potential (Ecell) of an electrochemical cell is given by the difference between the standard reduction potentials of the half-cells.
Ecell = E°(reduction at cathode) - E°(reduction at anode)
Given: E°(Al3+ + 3e- → Al) = 1.66 V
E°(Fe2+ + 2e- → Fe) = 0.44 V
We need to determine the cell potential for the following electrochemical system at 25C:
Al(s) | Al3+ (0.01 M) || Fe2+ (0.1 M) | Fe(s)
The cell diagram represents the two half-cells in the electrochemical cell. The two vertical lines represent the phase boundary between the two half-cells, and the double vertical line represents the salt bridge.
The half-cell reactions for the given electrochemical system are:
Al3+ + 3e- → Al (reduction at cathode)
Fe2+ → Fe + 2e- (oxidation at anode)
Step 1: Write the balanced cell reaction:
Al(s) + Fe2+ (0.1 M) → Al3+ (0.01 M) + Fe(s)
Step 2: Determine the reduction potential for the cathode:
E°(Al3+ + 3e- → Al) = 1.66 V
Step 3: Determine the oxidation potential for the anode:
E°(Fe2+ → Fe + 2e-) = -0.44 V (Note: The oxidation potential is the negative of the reduction potential.)
Step 4: Calculate the cell potential:
Ecell = E°(reduction at cathode) - E°(reduction at anode)
Ecell = 1.66 V - (-0.44 V)
Ecell = 2.10 V
However, this value is incorrect as the reduction potential for iron in the given electrochemical system is not standard. We need to use the Nernst equation to calculate the actual cell potential.
Step 5: Calculate the actual cell potential using the Nernst equation:
Ecell = E° - (RT/nF) ln(Q)
where,
E° = standard cell potential
R = gas constant = 8.314 J/mol K
T = temperature in Kelvin
n = number of electrons transferred
F = Faraday constant = 96,485 C/mol
Q = reaction quotient
At equilibrium, Q = K, the equilibrium constant.
K = [Al3+] / [Fe2+]
At 25°C, the equilibrium constant for the reaction is:
K = [Al3+] / [Fe2+]
K = (0.01 M) / (0.1 M)
K = 0.1
Substituting the values in the Nernst equation:
Ecell = E° - (RT/nF) ln(Q)
Ecell = 1.66 V - (0.0257 V) ln(0.1)
Ecell = 1.23 V
Therefore, the cell potential for the given electrochemical system at 25°C is 1.23 V.
Answer: Option (a) 1.23 V.
The cell potential for the following electrochemical system at 25°...