What is meant by EMF? EMF is the short form of Electromotive force, and it simply refers to the electrical activity produced by a non-electrical source. It is seen that devices provide emf by converting a form of energy into chemical energy. In chemistry, EMF means, the maximum potential difference between the two electrodes of a voltaic or galvanic cell. The devices that can produce an emf are electrochemical cells, thermoelectrical devices, solar cells, electric generators, and transformers.
EMF stands for Electromotive Force. It is defined differently in Physics and Chemistry. We will now study both the definitions and meaning in detail.
Now, what is EMF in Physics? EMF, in Physics, is defined as the energy per unit of an electric charge that is generated by an electric source, such as an electric generator or a battery. We can say that electromotive force or EMF is generated by any device that converts any other form of energy to electrical energy.
In chemistry, it simply means the maximum potential difference between the electrodes of a voltaic or galvanic cell.
In a simple way, if we try to understand an electrochemical cell, we can say that an electrochemical cell is a device that generates electricity from a chemical reaction. An electrochemical cell transforms chemical energy into electrical energy. In order to operate an electrochemical cell, a chemical reaction involving the exchange of electrons is required, such a reaction is known as a redox reaction. Generally, an electrochemical cell can be categorized into two types, and they are; Galvanic Cell and Daniell Cell.
Now, what is the galvanic cell? A galvanic cell is a device that was developed by an Italian scientist named, Luigi Galvani. It is an important electrochemical cell, and it forms the base of many other electrochemical cells. A galvanic cell is made up of two different kinds of electrodes which are immersed in their ionic solutions. Each of the two electrodes is called a half-cell, and a half-cell is not capable of producing the potential difference. Still, when both the electrodes or half-cells are combined, they can produce the required potential difference. The half-cells are connected using a salt bridge, this bridge provides the required amount of electrons to the electron deficit half-cell, and it also accepts the extra electrons from the electron-rich half-cell.
In simple words, a Daniell cell is a type of galvanic cell that is made using zinc and a copper electrode. Both the electrodes are immersed in their respective ionic solutions, i.e., for the zinc electrode, it is zinc sulfate, and for the copper electrode, it is copper sulfate. The zinc electrode is the anode, and the copper electrode is the cathode, both these half-cells are connected using a salt bridge to produce the maximum potential difference.
EMF, which is also known as the Electromotive force of a cell, is defined as the maximum potential difference between the electrodes of a cell. EMF of a cell or EMF of a galvanic cell can be calculated by taking the values of electrode potentials of both anode and cathode.
There are usually three ways of calculating the potential difference of a galvanic cell.
First, by observing the oxidation potential at anode and reduction potential cathode.
Second, by taking into account the reduction potential of both the electrodes.
Third, by taking into account the reduction potential of both the electrodes.
Cell notation or cell line notation is defined as the short-hand expression of any reaction of an electrochemical cell. In this type of expression, the anode and cathode of the cell are separated by using two bars or slashes that represents a salt bridge that connects the two electrodes. The individual solids, liquids, or aqueous solutions are separated using single bars.
Here is an example of cell notation.
Zn | Zn²⁺ || Cl¯ | AgCl | Agᐤ
The cell notation of an electrochemical reaction can also be expressed in the form of a chemical reaction by using the following steps.
For this purpose let us take the example of a cell notation.
Ag | Ag⁺ || H⁺ | H₂ | Pt
For the above cell notation, we first take the half-cell reaction of the anode:
Ag → Ag⁺ + e¯
Next, we take the reaction at the cathode:
2H⁺ + 2e¯ → H₂
We multiply both the reactions, and we get the final equation.
2Ag + 2H⁺ → 2Ag⁺ + H₂(g)
1. Explain the EMF of a Cell & Cell Notation.
Ans: EMF or Electromotive force of a cell is the maximum potential difference between the electrodes of a voltaic or galvanic cell. A galvanic cell has two electrodes one being the cathode and the other being the anode. The EMF is calculated by taking into consideration, the difference between the oxidation potential of one electrode and the reduction potential of another electrode. Cell notation in simple words means the short-hand expression of a reaction that takes place in an electrochemical cell. In this type of expression, the anode and cathode are separated by two bars which represent the salt bridge.
2. What is EMF of a Battery?
Ans: The electromotive force of a battery is the energy supplied by the battery per coulomb (Q) of charge passing through it. It is generally measured in volts (V). It is calculated by dividing the amount of energy supplied (E) by per coulomb of charge (Q). Hence the formula is;
ε = E/Q
Where ε is the EMF or Electromotive force,
E is the total amount of energy supplied and,
Q stands for per coulomb of charge that passes through the battery or cell.