Electrochemical series and standard Electrode potential

 Electrochemical series and standard electrode potential

Contents In this lesson are,

Introduction

Electrochemical series

An important concept of electrochemical series

Aspects of Electrochemical Series Applications

EMF calculation

Counting the degree of spontaneity in reactions

Gibbs Free Energy Calculation

Estimating a redox reaction's end result

Definition of Standard Electrode Potential

Standard Electrode Potential: Its Importance

Measurement of standard electrode potential

Uses of standard electrode potential

a) Redox Reactions' Spontaneity 

Introduction

Electrochemical series

In chemistry, the electrochemical series is also known as the active series. The periodic table's elements are organized in ascending order according to the electrode potential values they represent. The potential of different electrodes is observed using conventional hydrogen electrodes. Different ions are positioned in an electrochemical array according to their propensity for oxidation or reduction. Whether or not it is metallic. By carefully recording the voltage at the end of the standard hydrogen electrode and the half-cell attached to it, the value of the standard electrode potential is afterward determined.

In comparison to the Standard Hydrogen Electrode, the electrochemical series indicates how electropositive or electronegative the element/ion combination is. The name "half-cell" also applies to this combination. In the SHE, a metal that is more electropositive loses electrons more readily than hydrogen. A more electronegative material, however, has a greater ability to absorb electrons. Typically, an element that is more electronegative will absorb electrons from an element that is more electropositive. Thus, it can be claimed that the electrochemical series serves as a gauge of electronegative character.

Due to low reactivity, metals, like copper and gold, are referred to as "precious" metals and are used to manufacture coins and jewelry. A group of chemical elements grouped according to their standard electrode potentials is known as an electrochemical series. The potential of a cell with one electrode acting as the cathode and a standard hydrogen electrode (SHE) acting as the anode is known as electrode potential. Reduction always takes place at the cathode while oxidation always takes place at the anode.

An important concept of electrochemical series

By definition, hydrogen has an electrode potential of 0.00 (the Standard Hydrogen Potential, or SHE). In relation to it, all other potentials are defined.

High in the Electrochemical Series are the half-cells (element/ion pairs) having a very positive Electrode Potential. They are powerful oxidizing agents.

Reducing agents are the half-cells with negative electrode potential. The value is more negatively correlated with the decreasing power. Non-metals are electronegative, whereas metals are often electropositive.

The most reactive metals are those near the bottom. The non-metals at the top of the series, in contrast, are the most active. Reactivity is therefore lowest in the center. Metals towards the bottom of the series can reduce metals higher up.

Similar to metals, non-metals higher in the series have the ability to oxidize non-metals lower in the series.

Two half-cells are connected to each electrode in each electrochemical cell. One reaction involves oxidation and the other reduction in each half-cell. The oxidation potential and reduction potential are the respective potentials for each reaction.

The total of a cell's oxidative and reducing capacities is known as the cell EMF. It gauges how spontaneously the cell as a whole reacts. It serves as a gauge for how much work a cell can accomplish. By taking the half-cells' standard electrode potential values and adding them suitably, the electrochemical process aids in measuring the EMF cell.

Electrochemical Series

Aspects of Electrochemical Series Applications

a) EMF calculation

Two half-cells are connected to each electrode in each electrochemical cell. One reaction involves oxidation and the other reduction in each half-cell. The oxidation potential and reduction potential are the respective potentials for each reaction.

The total of a cell's oxidative and reducing capacities is known as the cell EMF. It determines how spontaneously the cell as a whole reacts. It serves as a measurement for how much work a cell can accomplish. By taking the half-cells' standard electrode potential values and adding them suitably, the electrochemical process aids in measuring the EMF cell.

E^ocell=E^ored– E^ooxi

where E^ored and E^oox represent the typical reduction potentials of the reducing and oxidizing half-cells, respectively.

b) Counting the degree of spontaneity in reactions

Reactive EMF cells are intimately correlated with the vitality or spontaneity of redox reactions:

The response is spontaneous if the cell EMF is positive; it is non-spontaneous if the cell EMF is negative. Therefore, by examining the reactants and products, we can determine whether a redox reaction can occur spontaneously. We formulate the equations for the half-reactions of reduction and oxidation. Then, adding in accordance with the electrochemical series, their standard electrode potentials. We can determine if a response is spontaneous based on the cellular EMF that results.

c) Gibbs Free Energy Calculation

Another indicator of a reaction's spontaneity is the Gibbs free energy (G⁰cell). The following is how it relates to the EMF unit (E unit).

G⁰cell =nFE⁰cell, where n is the number of involved electrons and F is the Faraday constant, which is equivalent to 96485 coulombs mol^-1.

Once more, based on the cellular EMF signal, we have:

• If the EMF source is positive, the reaction is spontaneous and the Gibbs free energy is positive; if the cell EMF is negative, the reaction is spontaneous and the Gibbs free energy is negative.

d) Estimating a redox reaction's end result

The ultimate product of the reaction can be calculated if using only the reactants, as shown below.

Using the electrochemical series, we put out the standard electrode potential values for each reactant. Then, we determine which has the greatest and least amount of potential for reduction. Once we know these numbers, we may make the following predictions about the outcome:

The cathode reduces the ion with the highest reduction potential, whereas the anode oxidizes the ion with the lowest reduction potential. The reaction's end result is provided to us by oxidized and reduced ions.

Standard Electrode Potential

A measurement of the potential for equilibrium is the standard electrode potential. The potential of the electrode is the difference in potential between the electrode and the electrolyte. The electrode potential is referred to as the standard electrode potential when unity represents the concentrations of all the species involved in a semi-cell.

Definition of Standard Electrode Potential

In an electrochemical cell, the standard electrode potential occurs at, for example, 298 K, 1 atm of pressure, and 1 M of concentration. The typical electrode potential of a cell is denoted by the symbol "E^ocell."

Standard Electrode Potential: Its Importance

Redox reactions, which are composed of two half-reactions, constitute the foundation of all electrochemical cells.

At the anode, there is an oxidation half-reaction that results in an electron loss.

At the cathode, a reduction event occurs that results in an electron gain. The anode to the cathode is where the electrons move as a result.

The difference in the individual potentials of each electrode causes an electric potential to develop between the anode and the cathode (which are dipped in their respective electrolytes).

With the aid of a voltmeter, the cell potential of an electrochemical cell can be determined. A half-individual cell's potential, however, cannot be precisely quantified on its own.

It's also critical to remember that this potential can alter in response to modifications in pressure, temperature, or concentration.

The requirement for standard electrode potential emerges in order to acquire the individual reduction potential of a half-cell.

With the use of a reference electrode known as the standard hydrogen electrode, it is measured (abbreviated to SHE). SHE has an electrode potential of 0 volts.

By connecting an electrode to the SHE and measuring the cell potential of the resulting galvanic cell, the standard electrode potential of the electrode can be determined.

An electrode's oxidation potential is the polar opposite of its reduction potential. As a result, an electrode's standard reduction potential can be used to define its standard electrode potential.

High standard reduction potentials are exhibited by good oxidizing agents, whereas low standard reduction potentials are exhibited by good reducing agents.

Ca2+ has a standard electrode potential of -2.87 V, while F2 has a standard electrode potential of +2.87 V. This suggests that Ca is a reducing agent while F2 is an excellent oxidizing agent.

Measurement of standard electrode potential

The Standard Hydrogen Electrode (SHE) is coupled to a metal (or non-metal) electrode that contains its ion. H2 and H+ ions make up SHE. Under normal circumstances, a certain value of voltage is seen across the electrodes depending on the type of metal and ions used. For the specific metal/ion pairing, this is known as the "standard electrode potential value."

Uses of standard electrode potential

a)Redox Reactions' Spontaneity

The Gibbs free energy, or "G^o," must be negative if a redox reaction occurs on its own. The following equation provides an explanation:

G^ocell = -nFE⁰cell

F is Faraday's constant, and n is the total number of moles of electrons created for every mole of product (approximately 96485 C.mol-1).

The following equation can be used to determine the E⁰cell:

E⁰cell = E⁰cathode – E⁰anode

As a result, the E⁰cell can be calculated by deducting the cathode's standard electrode potential from the anode's. Because both n and F have positive positive values and the G^o value must be negative, the E⁰cell must be positive for a redox reaction to be spontaneous.

This suggests that during an unplanned process,

Since E⁰cell > 0, it follows that E⁰cathode > E⁰anode.

Thus, the cathode and anode's typical electrode potentials can be used to estimate how spontaneously a cell response would occur. It should be noted that the cell's " G^o " in electrolytic cells is positive while the cell's "G^o" in galvanic cells is negative.