The Emf or electromotive force is a term used to depict the potential difference and is not a term related to force and it is measured in volt. It was invented by Alessandro Volta when he first invented the battery. And also he mentioned the contact of electrode and electrolyte is responsible for the emf not mentioned chemical reactions. In 1830 Michael Faraday ascertained that the chemical reactions taking place at the electrode and electrolyte interface are responsible for the emf. It is a characteristic of all the energy sources that have a circuit in them. The electromotive force also has an abbreviation of E but the common representation is emf.
The utmost potential difference between the two electrodes of the cell when the circuit is open is emf or electromotive force. It is a source of emf. It is the characteristics of a particular cell so does not depends on the amount of current drawn from the cell. That is independent of the amount of current. So the value of emf is always constant and is present even if the current is not supplied. Or it is the maximum voltage that a battery can provide. The instrument used for the determination of electromotive force is an emf meter. The maximum potential or emf of a galvanic cell is always a constant value. And the value is 1.100V for 1M concentration. A galvanic cell is,
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Emf or electromotive force of cells can be defined as the net voltage that prevails between the oxidation and reduction of half cells of a particular cell. And the value of emf of a particular cell is always a constant. The potential difference between the two electrodes of the galvanic cell or the emf is measured in the unit volt.
Emf or electromotive force is the terminal potential difference of batteries when no current flows through them. It is the quantity of energy provided by the battery for every coulomb of charge enacting through it. Emf of cells is measured by measuring the voltage present in the cells using a voltameter and measuring the current in the circuit using an ammeter at various resistance.
$$\mathrm{emf = I(r+R)}$$
Emf is the net electrode potential developed on the anode and cathode electrodes of an electrochemical cell in which oxidation and reduction are happening when no current is supplied. These electrodes are also called half cells. The value of emf depends on the nature of the electrolyte and electrode present in a particular cell. And is always a constant for a particular concentration. For a standard hydrogen electrode or SHE, the value of emf is always zero volts. This electrode is used for the determination of emf of other electrodes by pairing with it.
The cell that is capable of generating electricity through chemical reactions or chemical reactions with the help of electricity is an electrochemical cell. There is no evolvement of heat by the electrochemical cells. There are mainly two types of electrochemical cells. They are voltaic or galvanic cells and electrolytic cells. The production of electrical energy with the help of chemical reactions is a galvanic cell or voltaic cell. And the one which involves the generation of chemical reactions with the help of electricity is the electrolytic cell. These cells have two types of electrodes they are anode and cathode. The anode is a negative electrode where oxidation takes place which is the loss of electrons. While cathode is a positive electrode in which reduction takes place that is acceptance of electron occurs.
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The name galvanic cell is provided to the type of electrochemical cell by the scientist Luigi Galvani. This type of electrochemical cell can generate electricity by the conversion of chemical energy to electricity. It contains two types of electrodes, an electrolyte and a salt bridge to connect the two electrodes. An example of a galvanic cell is the Daniel cell.
Daniel cell is a type of electrochemical cell that can be used for the generation of electricity with the help of chemical reactions. In the Daniel cell Zinc is used as the anode and Copper is the cathode. The Zinc electrode is dipped in the Zinc sulfate solution and a Copper electrode is dipped in the Copper sulfate solution. The electrode at which oxidation takes place is the anode.
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And the reaction is,
$$\mathrm{Zn(s)\to Zn^{2+}(aq)+2e^{-}}$$
And the electrode at which reduction takes place is Copper. And the reaction is,
$$\mathrm{Cu^{2+}(aq)+2e^{-}\to Cu(s)}$$
The overall reaction is,
$$\mathrm{Zn(s)+Cu^{2+}(aq)\to Zn^{2+}(aq)+Cu(s)}$$
The use of symbols and an abbreviation of elements for representing the half cells of an electrochemical cell is a cell notation. The cell notation must follow some guidelines for proper representation. Some rules can give a proper representation. They are,
Chemical formulas and symbols of a chemical compound can be used for the representation.
The first part of cell notation represents the anode electrode and then the cathode electrode.
The chemical reactions that are happening in the two half cells are separated using a parallel line. And it represents a salt bridge.
For every chemical compound, the phases are represented with the help of some symbols such as 's' for solid, 'l' for liquid, and 'g' for gases.
As cell notation is a representation of two half cells of an electrochemical cell That is anode and cathode reactions. With the help of cell notation, we can write the oxidation and reduction reactions of a particular cell. As the first part represents the oxidation reaction and the second part represents the reduction reaction we can derive these equations easily. For example, the Daniel cell is represented by,
$$\mathrm{Zn(s)\left|Zn^{2+}(aq) \right|\left|Cu^{2+}(aq) \right|Cu(s)}$$
From which the oxidation reaction can be derived since the first part represents the anode electrode. And where the loss of electrons is taking place. The reaction is,
$$\mathrm{Zn(s)\to Zn^{2+}(aq)+2e^{-}}$$
And the second part represents the cathode electrode and the reaction is a reduction. The equation can be easily obtained since it is a reduction, so the gain of electrons is happening. The equation is,
$$\mathrm{Cu^{2+}(aq)+2e^{-}\to Cu(s)}$$
Emf or electromotive force is the potential difference between two electrodes when the circuit is open. That is a net potential developed when no current flows through it. And is a constant value for a particular concentration. An electrochemical cell is a type of cell where the generation of electricity by chemical reaction or chemical reaction with the help of electricity is happening. Galvanic or volcanic cells and electrolytic cells are two types of electrochemical cells. Daniel's cell is an example of a galvanic cell. Where the generation of electricity takes place with the help of two types of electrodes Zinc and Copper. The simple shorthand representation of all the reactions happening in electrochemical cells is done with the help of cell notations. From which the half cell equation can also be derived.
Q1. How do potential differences differ from emf?
Ans. As the name itself depicts it is the difference in potential at any two points in a closed circuit that contains the flow of electricity. So current is required for the calculation of potential difference.
Q2. What is an example of an electrolytic cell?
Ans. An example of an electrolytic cell is a cell made of sodium chloride in which sodium metal and chlorine gas are obtained by the supply of electricity.
Q3. Is the battery a galvanic cell?
Ans. The battery is an example of a galvanic cell that contains a string or combination of several galvanic cells.
Q4. What is the source of emf?
Ans. The sources of emf are generator, electrochemical cell, and battery.
Q5. What is a positive electrode?
Ans. The electrode in which that contains a higher potential is positive and is a cathode. And is represented on the right side of an electrochemical cell. While the negative electrode on the left side is the anode.
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