Standard electrode potential and electrochemical series

In electrochemistry, the terms "standard electrode potential" and "electrochemical series" are fundamental. These concepts allow us to understand and predict how different chemical species accept or donate electrons in redox reactions. This article explains these topics in detail, providing fundamental understanding and illustrative examples.

Understanding standard electrode potential

The standard electrode potential is a measure of the individual potential of a reversible electrode under standard state conditions, including solutes at an activity of 1 mol/L, gases at a pressure of 1 atmosphere, and a temperature of 25°C (298 K). This potential is important in determining the tendency of a chemical species to be reduced or oxidized.

The standard electrode potential is represented by E° and is measured in volts (V). It compares the ability of different electrodes to drive electrons and thus carry out redox reactions.

The standard hydrogen electrode (SHE) serves as a reference electrode, with a set potential of 0.00 V. All other electrode potentials are measured relative to this standard.

The role of the standard hydrogen electrode

Standard Hydrogen Electrode (SHE) is important in defining standard conditions and measuring electrode potentials. The SHE consists of a platinum electrode immersed in a solution of hydrochloric acid with hydrogen gas bubbled through it. The setup is shown below:

The SHE is considered the baseline at 0.00 V. All other electrode potentials are measured against this baseline. This forms the basis of the electrochemical series, which ranks elements based on their standard electrode potentials.

Calculating cell potential using standard electrode potential

A galvanic cell uses two different metals that are connected by a salt bridge or porous membrane, causing ions to flow and produce an electrical current. The standard cell potential, E° cell, is calculated using the equation:

E° cell = E° cathode - E° anode

Where:

• E° cathode is the standard potential for the reduction reaction taking place at the cathode.
• E° anode is the standard potential for the oxidation reaction taking place at the anode.

Zn(s) | Zn 2+ (aq) || Cu2 + (aq) Cu(s)

The reactions are as follows:

• At anode: Zn(s) → Zn 2+ (aq) + 2e⁻ (standard potential = -0.76 V)
• At cathode: Cu 2+ (aq) + 2e⁻ → Cu(s) (standard potential = +0.34 V)

The overall cell potential is calculated as:

E° cell = 0.34 V – (-0.76 V) = 1.10 V

This positive potential indicates that the reaction is spontaneous.

Electrochemical series and its importance

The electrochemical series, also known as the activity series, is a list of elements ordered according to their standard electrode potential. This series helps to predict and understand the behavior of metals during redox reactions.

This series is based on the standard electrode potential of each metal, making it easy to predict how easily the metal will lose electrons, i.e., undergo oxidation. Metals at the top, such as lithium, have the highest tendency to oxidize, while metals at the bottom, such as gold, are more likely to be reduced.

        Li⁺/Li < -3.05 V
        K⁺/K < -2.93 V
        Na⁺/Na < -2.71 V
        Ca2⁺/Ca2 < -2.87 V
        ,
        Cu2⁺/Cu2 < +0.34 V
        Ag⁺/Ag < +0.80 V
        Au3⁺/Au < +1.50 V
    

Metals higher in the series can displace metals lower in the series from their compounds in aqueous solution.

        Zn(s) + CuSO 4 (aq) → ZnSO 4 (aq) + Cu(s)
    

Applications of electrochemical series

There are many practical applications of the electrochemical series:

Predicting the feasibility of a response

This series enables chemists to predict the feasibility of redox reactions. A positive cell potential indicates that the reaction is spontaneous.

        Cu²⁺(aq) + Zn(s) → Cu(s) + Zn²⁺(aq)
    

Understanding corrosion

Corrosion is a redox process in which metals are slowly oxidized by their environment. The electrochemical series helps to understand and prevent corrosion. For example, the tendency of iron to rust can be reduced by using more active metals such as zinc for galvanization.

Electromotive force(EMF) calculation

Through the electrochemical series the emf of electrochemical cells can be calculated, which is helpful in the design and application of batteries.

Manufacture of chemicals

The electrochemical series is used in the industrial preparation of chemicals. For example, it helps determine the proper choice of metals in electrolysis processes, such as the extraction of sodium and chlorine from sodium chloride through electrolysis.

Conclusion

Understanding standard electrode potentials and the electrochemical series is essential to understanding electrochemical reactions. By understanding these concepts, predict which reactions are likely to occur spontaneously and use this knowledge in a variety of scientific and industrial applications. Remember, these concepts reveal the underlying behavior of metals and ions in various scenarios, providing foundational insights for electrochemistry and its applied fields.

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