The e.m.f. of a galvanic cell with electrode potentials of Al equal to...
Galvanic Cell:
A galvanic cell consists of two half-cells, each of which contains an electrode immersed in an electrolyte solution. The two half-cells are connected through a wire and a salt bridge.
Electrode Potential:
The electrode potential is the measure of the tendency of a metal electrode to lose or gain electrons. The standard electrode potential is a measure of the tendency of a metal electrode to lose electrons when it is in contact with its own aqueous ions.
Calculation of e.m.f.:
The e.m.f. of a galvanic cell is given by the difference in the electrode potentials of the two half-cells. The half-cell with the higher electrode potential will act as the cathode, and the half-cell with the lower electrode potential will act as the anode.
Given:
Electrode potential of Al = -1.66 V
Electrode potential of Mg = -0.54 V
The half-cell with the higher electrode potential is Mg, and it will act as the cathode.
The half-cell with the lower electrode potential is Al, and it will act as the anode.
Therefore, the e.m.f. of the galvanic cell will be:
e.m.f. = (Electrode potential of cathode) - (Electrode potential of anode)
e.m.f. = (-0.54 V) - (-1.66 V)
e.m.f. = 1.12 V
Hence, the correct option is (D) -1.12 V.
The e.m.f. of a galvanic cell with electrode potentials of Al equal to...
Calculation of e.m.f of the galvanic cell
Given electrode potentials:
• E°(Al) = -1.66 V
• E°(Mg) = -0.54 V
The e.m.f of the galvanic cell can be calculated using the Nernst equation
Ecell = E°cell - (RT/nF) lnQ
where,
• E°cell is the standard electrode potential of the cell.
• R is the gas constant (8.314 J K-1 mol-1).
• T is the temperature in Kelvin.
• n is the number of electrons transferred in the cell reaction.
• F is the Faraday constant (96,485 C mol-1).
• Q is the reaction quotient.
The reaction taking place in the cell is:
Al(s) + Mg2+(aq) → Al3+(aq) + Mg(s)
The cell reaction can be split up into two half-cells:
Al3+(aq) + 3e- → Al(s) (reduction half-cell)
Mg2+(aq) + 2e- → Mg(s) (oxidation half-cell)
The standard cell potential can be calculated using:
E°cell = E°reduction - E°oxidation
E°cell = (-1.66 V) - (-0.54 V)
E°cell = -1.12 V
The reaction quotient Q can be calculated using the concentrations of the reactants and products:
Q = [Al3+]/[Mg2+]
At equilibrium, Q = Kc, where Kc is the equilibrium constant.
Assuming the concentrations of Al3+ and Mg2+ are both 1 M, the value of Q can be calculated as:
Q = [Al3+]/[Mg2+] = 1/1 = 1
Using the values of E°cell, R, T, n, F, and Q, the e.m.f of the galvanic cell can be calculated as:
Ecell = E°cell - (RT/nF) lnQ
Ecell = -1.12 V - [(8.314 J K-1 mol-1) (298 K) / (3 mol e-)(96,485 C mol-1)] ln(1)
Ecell = -1.12 V
Therefore, the e.m.f of the galvanic cell is -1.12 V.
The correct answer is option (d) -1.12 V
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