EMF of a Galvanic Cell and its Measurement

EMF of a galvanic cell measures the maximum potential difference between two electrodes in a cell. Alternatively, it can be defined as the difference between the oxidation and reduction half-reactions. Galvanic cells are primarily determined by their electromotive force. Electrical energy is generated by electrochemical cells, which convert chemical energy into electricity. Moreover, galvanic cells are commonly referred to as voltaic cells. Galvanic cells work purely on the basis of Gibbs energy from spontaneous redox reactions.

Electrochemical cells may be found in many aspects of our life, from disposable AA batteries in remote controls to lithium-ion batteries in iPhones to nerve cells sprinkled throughout our bodies. Galvanic, sometimes known as Voltaic, and electrolytic cells are the two types of electrochemical cells. Electrolytic cells rely on an external power source, such as a DC battery or an AC power source, whereas galvanic cells use spontaneous redox reactions. An anode, a cathode, and an electrolyte, in which the two electrodes are submerged, will be used in galvanic and electrolytic cells, respectively.

Electromotive Force (EMF)

Electromotive force is defined as the electric potential produced by either electrochemical cell or by changing the magnetic field. The electromotive force is the work done on a unit of electric charge or the energy gained per unit of electric charge. The property of any energy source capable of pushing an electric charge around a circuit is called electromotive force.

Galvanic Cells

As DC power sources, galvanic cells are usually used. A basic galvanic cell may just have one electrolyte separated by a semipermeable membrane, or a more complicated version may have two half-cells connected by a salt bridge. The salt bridge is made up of an inert electrolyte, such as potassium sulfate, whose ions flow into the individual half-cells to balance the charges that are building up at the electrodes. During electrolysis, the anode is oxidized, and the cathode is reduced. The anode is the negative terminal of the galvanic cell because the reaction at the anode provides the source of electrons for the current. The galvanic cell is also called a voltaic cell, For example, Daniell Cells.

Electromotive Force of Galvanic Cells

The electrical potential difference (commonly referred to as voltage) between two electrodes can be measured by a voltmeter in order to determine just how spontaneous a redox reaction is. Potential differences are usually expressed in volts (V), an SI unit equaling one joule per ampere-second.

A voltage measure indicates the likelihood of current flowing in an external circuit. It indicates how strongly electrons can be pushed into the circuit by the anode reaction and how strongly they can be withdrawn by the cathode reaction.

When the external circuit is blocked by a large electrical resistance, a large potential difference is observed. An emf is an electromotive force, also called a potential difference, which can be measured for a given cell.

The Electromotive Force, or EMF, is given a positive value if the electrode on the left pushes electrons into the external circuit and the electrode on the right pulls them out, the cell EMF is displayed on the voltmeter dial. The cell emf is minus the meter reading if the half-cell on the right side of the abbreviated cell notation is releasing electrons, rendering the right-hand terminal of the voltmeter negative. This is equivalent to a conventionally worded non spontaneous cell response.

If the cell reaction is spontaneous by convention, the EMF is assigned a positive value when written in shorthand notation. The cell EMF is indicated on the voltmeter dial if the electrode on the left pushes electrons into the external circuit and the electrode on the right takes them out. If the half-cell on the right side of the shortened cell notation is releasing electrons, the cell EMF is minus the meter reading, making the right-hand terminal of the voltmeter negative. This is the same as a nonspontaneous cell response in the traditional sense.

How is the Electromotive Force of a Galvanic Cell Calculated?

A galvanic cell consists of two half-cells. An oxidation cell’s cathode is placed on the right, and the reduction cell’s cathode on the left, in accordance with convention.

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

Oxidation: Zn(s) → Zn²⁺(aq) + 2e⁻

Reduction: Cu²⁺(aq) + 2e⁻ → Cu(s)

The following are the simplest steps for calculating the EMF of a galvanic cell.

1. Split the redox reaction into half-reactions for reduction and oxidation.
2. Calculate the standard reduction potentials for the half-reactions.
3. Reverse reaction
4. To find the total cell EMF, E0cell, add the two E0 together 
5. Determine if the reaction is galvanic.

Conclusion 

From this article, students will understand concepts such as standard emf of a galvanic cell, galvanic cell measurement formulas & how to calculate emf of a galvanic cell. Students will learn how to compute the electrode potential of a half cell and a complete cell. Students will also learn how the electrode potential fluctuates depending on the concentration of electrolytes in the anodic and cathodic halves of the cell.