Electrode Potential and Energy Quiz

Electrical Energy and Electrode Potential

• Electrical energy is the product of voltage and coulombs.
• Total charge is determined by the number of moles of electrons passing through a circuit.
• Total charge is calculated as the product of the number of moles of electrons (n) and Faraday's constant (F), which represents the charge contained in one mole of electrons.
• Maximum electrical work (Wmax) is equal to the electrical work (Wele) and is calculated as -nFE, where E is the electrode potential.
• The negative sign indicates that the electrical work is done by the system on the surroundings.
• Maximum work is equal to the change in free energy (ΔG).
• The free energy change due to the transfer of one mole of ions across the double layer is related to the electrode potential, with ΔG = -nFE.
• For spontaneous processes, ΔG is negative, and E is positive, as both n and F are positive.

Standard Electrode Potential and Nernst Equation

• For reactions where reactants and products are in their standard states, ΔGo = -nFEo.
• The standard electrode potential (Eo) is positive for spontaneous processes.
• ΔG is related to ΔGo and the equilibrium constant (Kc) by the equation ΔG = ΔGo + RT lnKc.
• This equation can be rearranged to express the electrode potential (E) in terms of the standard electrode potential (Eo) and the concentrations of the oxidized and reduced forms: E = Eo - (RT/nF) ln([M]/[Mn+]).
• For a metal electrode, [M] = 1, and the equation simplifies to the Nernst equation: E = Eo + (RT/nF) ln[Mn+].

Effect of Concentration and Temperature

• The single electrode potential is directly proportional to both the metal ion concentration and the temperature, as these terms appear in the numerator of the Nernst equation.

Galvanic Cells and Electrode Reactions

• A galvanic cell is formed when two electrodes in contact with suitable electrolytes are connected externally by a conducting material and internally by a salt bridge, generating an electric current.
• Liquid-liquid contact between different electrolyte solutions introduces an additional potential called the liquid junction potential.
• This potential can be reduced by connecting the electrolyte compartments through a salt bridge, where the liquid-liquid junction potentials at either end cancel out.
• The electrode where oxidation occurs is called the anode, while the electrode where reduction occurs is called the cathode.

Daniel Cell Example

• The Daniel cell can be represented as Zn(s) | ZnSO4(aq) || CuSO4(aq) | Cu(s).
• At the anode: Zn(s) → Zn++(aq) + 2e− (oxidation).
• At the cathode: Cu++(aq) + 2e− → Cu(s) (reduction).
• Overall reaction: Zn(s) + Cu++(aq) → Zn++(aq) + Cu(s).
• In a galvanic cell, the cathode has a higher potential than the anode.

EMF of a Cell

• The potential difference between the two electrodes in a cell is called the cell potential or EMF (electromotive force), represented as 'EMF,' 'emf,' or 'Ecell.'
• The cell potential is measured in volts and is larger when a given number of electrons can do a large amount of work.
• The cell potential becomes zero when the overall cell reaction is at equilibrium, and the cell can no longer do work.
• The EMF of a cell is the difference in the single electrode potentials of the two electrodes: Ecell = Ecathode - Eanode.
• The cell potential can also be expressed in terms of the standard cell potential and the ratio of products to reactants: Ecell = Eocell + (0.0591/n) log10([Products]/[Reactants]).

Measurement of Single Electrode Potential

• Single electrode potentials cannot be measured directly.
• To determine a single electrode potential, the electrode is coupled with a standard reference electrode, such as a calomel electrode.
• The cell potential (Ex) is measured, and since the potential of the reference electrode (Ecalomel) is known, the potential of the unknown electrode (e.g., Ezn++|Zn) can be calculated: Ezn++|Zn = Ecalomel - Ex.

Cell Notation and Cell Conventions

• Phase boundaries (metal-solution interfaces) are denoted by a vertical line (|).
• A double vertical line (||) represents the salt bridge.
• An arrow indicates the flow of electrons.
• The anode is written on the left side of the cell notation, while the cathode is on the right.

Sign Conventions

• The electrode potential is generally expressed as a reduction potential.
• The electrode at which reduction occurs with respect to the standard hydrogen electrode has a positive reduction potential and a negative oxidation potential.
• The electrode at which oxidation occurs with respect to the standard hydrogen electrode has a positive oxidation potential and a negative reduction potential.

Calomel Electrode

• The calomel electrode is represented as Hg | Hg2Cl2(sat), KCl(solution).
• The reaction at the calomel electrode: ½ Hg2Cl2(s) + e−  Hg(l) + Cl−(aq).
• The electrode potential of the calomel electrode depends on the concentration of KCl solution used.

Silver-Silver Chloride Electrode

• The silver-silver chloride electrode is frequently used as a reference electrode for accurate potential measurements.
• It is constructed by coating a platinum wire with silver and then partially converting it to silver chloride.
• The electrode is reversible with respect to chloride ions and can be represented as Ag(s) | AgCl(s), KCl(aq).
• The reaction: Ag(s) + Cl−(aq)  AgCl(s) + e−.
• The potential of the silver-silver chloride electrode is 0.2224V at 25oC (1M KCl) and 0.199V at 25oC (saturated KCl).

Ion Selective Electrodes

• Ion selective electrodes respond to specific ions in a solution, ignoring others.

Test your understanding of electrical energy, electrode potential, and the Nernst equation. This quiz covers key concepts such as maximum electrical work, charge calculations, and the relationship between free energy and electrode potential. Perfect for reinforcing your knowledge of electrochemistry principles.