standard electrode potential

(noun)

An electrode potential measured under standard conditions (298 K, 1 atm, and 1 M).

Examples of standard electrode potential in the following topics:

  • Predicting Spontaneous Direction of a Redox Reaction

    • To figure this out, it is important to consider the standard electrode potential, which is a measure of the driving force behind a reaction.
    • The sign of the standard electrode potential indicates in which direction the reaction must proceed in order to achieve equilibrium.
    • What happens to the standard electrode potential when the reaction is written in the reverse direction?
    • Neither the relative strengths of the oxidizing or reducing agents nor the magnitude of the potential will change.
    • However, what will change is the sign of the standard electrode potential.
  • Free Energy and Cell Potential

    • Electricity is generated due to the electric potential difference between two electrodes.
    • In electrochemistry, the standard electrode potential, abbreviated E°, is the measure of the individual potential of a reversible electrode at standard state, which is with solutes at an effective concentration of 1 M, and gases at a pressure of 1 atm.
    • Since the standard electrode potentials are given in their ability to be reduced, the bigger the standard reduction potentials, the easier they are to be reduced; in other words, they are simply better oxidizing agents.
    • For example, F2 has a potential of 2.87 V and Li+ has a potential of -3.05 V.
    • In the example of Zn2+, whose standard reduction potential is -0.76 V, it can be oxidized by any other electrode whose standard reduction potential is greater than -0.76 V and can be reduced by any electrode with standard reduction potential less than -0.76 V.
  • Electrolytic Properties

    • In other systems, the electrode reactions can involve electrode metal as well as electrolyte ions.
    • In order to determine which species in solution will be oxidized and which will be reduced, the standard electrode potential of each species may be obtained from a table of standard reduction potentials, a small sampling of which is shown here:
    • Historically, oxidation potentials were tabulated and used in calculations, but the current standard is to only record the reduction potential in tables.
    • This is the standard reduction potential for the reaction shown, measured in volts.
    • Use a table of standard reduction potentials to determine which species in solution will be reduced or oxidized.
  • Standard Reduction Potentials

    • Standard reduction potentials provide a systematic measurement for different molecules' tendency to be reduced.
    • The standard reduction potential is defined relative to a standard hydrogen electrode (SHE) reference electrode, which is arbitrarily given a potential of 0.00 volts.
    • The values below in parentheses are standard reduction potentials for half-reactions measured at 25 °C, 1 atmosphere, and with a pH of 7 in aqueous solution.
    • Historically, many countries, including the United States and Canada, used standard oxidation potentials rather than reduction potentials in their calculations.
    • These are simply the negative of standard reduction potentials, so it is not a difficult conversion in practice.
  • Electrochemical Cell Notation

    • Recall that standard cell potentials can be calculated from potentials E0cell for both oxidation and reduction reactions.
    • A positive cell potential indicates that the reaction proceeds spontaneously in the direction in which the reaction is written.
    • Conversely, a reaction with a negative cell potential proceeds spontaneously in the reverse direction.
    • One beaker contains 0.15 M Cd(NO3)2 and a Cd metal electrode.
    • The other beaker contains 0.20 M AgNO3 and a Ag metal electrode.
  • Predicting if a Metal Will Dissolve in Acid

    • A metal is soluble in acid if it displaces H2 from solution, which is determined by the metal's standard reduction potential.
    • The sign of this potential difference depends on the direction (oxidation or reduction) in which the electrode reaction proceeds.
    • Therefore, the half-cell potential for the Zn/Zn2+ electrode always refers to the reduction reaction:
    • These values can be determined using standard reduction potentials, which can often be looked up.
    • Using the standard reduction potentials of a reaction, one can determine how likely a given metal is to accept or donate electrons.
  • Van de Graff Generators

    • Using a moving belt, it can create extremely high potential differences.
    • Two electrodes are positioned near the bottom of the lower pulley and inside the sphere, over the upper pulley.
    • In this figure, a high, positive DC potential is applied to the upper roller.
    • Final potential is proportional to the size of the sphere and its distance from the ground.
    • Numbers in the diagram indicate: 1) hollow metal sphere; 2) upper electrode; 3) upper roller (for example an acrylic glass); 4) side of the belt with positive charges; 5) opposite side of the belt with negative charges; 6) lower roller (metal); 7) lower electrode (ground); 8) spherical device with negative charges, used to discharge the main sphere; 9) spark produced by the difference of potentials
  • Principles of Electricity

    • This process, called action potential, underlies many nervous system functions.
    • Voltage is the measure of potential energy generated by separated charge.
    • Voltage may represent either a source of energy (electromotive force) or lost or stored energy (potential drop).
    • In electrically active tissue, the potential difference between any two points can be measured by inserting an electrode at each point and connecting both electrodes to to a specialized voltmeter.
    • These concentration gradients provide the potential energy to drive the formation of the membrane potential.
  • The Battery

    • One half-cell includes electrolyte and the anode, or negative electrode; the other half-cell includes electrolyte and the cathode, or positive electrode.
    • The electrodes do not touch each other but are electrically connected by the electrolyte.
    • A battery stores electrical potential from the chemical reaction.
    • Electric potential is defined as the potential energy per unit charge (q).
    • The voltage, or potential difference, between two points is defined to be the change in potential energy of a charge q moved from point 1 to point 2, divided by the charge.
  • Other Rechargeable Batteries

    • NiMH batteries use positive electrodes of nickel oxyhydroxide (NiOOH), as does the NiCd, but the negative electrodes use a hydrogen-absorbing alloy instead of cadmium.
    • The lithium-ion battery is a family of rechargeable batteries in which lithium ions move from the negative electrode to the positive electrode during discharge, and back when charging.
    • The negative electrode of a conventional lithium-ion cell is made from carbon.
    • The positive electrode is a metal oxide, and the electrolyte is a lithium salt in an organic solvent.
    • The advantages of LiPo over the lithium-ion design include potentially lower cost of manufacture, adaptability to a wide variety of packaging shapes, reliability, and ruggedness.
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