galvanic cell (T.^[1][2][3] Galvani) also called the voltaic cell is a battery invented by the Italian scientist Professor Luigi Galvani (pronounced Luigi Galvani) Professor of Medicine at the University of Bologna and discovered by chance in 1786 during his experiments on the action of electricity on the muscles of frogs where he noticed the frog’s trembling in one of his experiments when its two ends touched two different metals in a circle He thought that the source of electricity was due to animal electricity, until the physics professor Alessandro Volta came, who attributed the emergence of electricity to the fact that the two metals are different. Volta was able later to make a battery of this type, and these cells were named after the first person who discovered this phenomenon, a galvanic.

Description of the galvanic cell[عدل]

A galvanic cell consists of two halves of cells. In each of them, a different metal electrode is immersed, as in the figure, one of the electrodes is made of Zn and the other is made of Cu. Each of them is immersed in a solution of one of its salts: zinc in a solution of zinc sulfate ZnSO₄ and a copper plate in a copper sulfate CuSO solution₄. The chemical property here is that the metal atoms have a tendency to leave the metal and enter the solution, and when they do so, they leave electrons on the board and enter the solution in the form of positively charged ions. Each of the two half-cells has its interaction with its solution. This system is named after the first person invented by Daniel, and that cell is called the Daniel cell.

As in the figure, we find that the Zn atoms have a greater tendency to enter their solution than the Cu atoms. That is, the accumulation of electrons on the zinc plate is greater than the accumulation on the copper plate. Since the electrons have a negative charge, a negatively charged electric potential is formed on the zinc plate, which is greater than the electrical potential on the copper plate. Since there is no external connection between the two electrodes, no current flows and electrons do not move.

When we connect the two poles from the outside (with a voltmeter as in the figure), the electrons begin to move from the more negative Zn pole to the more positive (positive) Cu pole. Since the electrons have a negative charge, an electric current is produced that runs in the opposite direction of the electrons. At the same time, a current of ions travels in the solution with the same strength as the external current. For every two electrons leaving the zinc electrode in the outer circle to the copper electrode, a Zn atom enters the solution in the form of a Zn positive ion²⁺ This is to compensate for the two electrons that left the zinc plate from the outside.

According to the definition, the anode is the electrode on which oxidation (the loss of electrons) occurs. Therefore, in the galvanic cell, the zinc electrode represents the anode. Since copper has gained two electrons through the external conduction, it also gives two electrons to the Cu ion²⁺ From the copper sulfate solution, the copper ion neutralizes and is deposited on the copper plate. By definition, the cathode is the electrode on which reduction (i.e. gaining electrons) takes place, and the copper electrode is the cathode. Electrons travel from the anode to the cathode in the external electrical circuit.

Calculating the electromotive force[عدل]

The cell’s potential difference (emf) can be determined by the standard electrode potential table of the elements for both halves of the cell. When making this designation, we assume that the current passing between the two poles of the cell is zero.

We start first by choosing the two metals. We look in the standard electrode potential for the standard electrode potential for each of the two metals E^o It is given in the table in volts. The cell potential difference is equal to the product of subtracting the two measured voltages.

For example, in the figure above, we have two solutions of copper sulfate and zinc sulfate, and a copper plate is immersed in copper sulfate just as a zinc plate is immersed in a zinc sulfate solution. There is also a bridge between the two solutions (and this can be replaced by a separating membrane between the two solutions) that allows the passage of SO ions₄²⁻ From a copper solution to a zinc solution (this is how the electrical circuit is completed when the two plates are connected from the outside with a conductor.)

We have two half cells, one for Cu and the other for Zn, and the two reactions taking place are:

Reaction at the anode:

Zn → Zn²⁺+2e^– (E = +0.76 V)

Reaction at the cathode:

Cu²⁺ +2e^– → With (E = +0.34 V)

For the copper half cell, we obtained the reduction potential E = +0.34 V or the oxidation potential E = -0.34 V for the cathode

For half a zinc cell, the oxidation potential E = +0.76 V or the reduction potential E = -0.76 V for the anode.

From the table of the electrochemical series. That is, the overall reaction taking place in the cell:

Cu²⁺ + Zn → Cu + Zn²⁺

And we get the cell potential difference by subtracting: the anode oxidation potential (anode) – the cathode oxidation potential (cathode)

+0.76 – (- V 1.100 = (0.34

Or from the subtraction: the cathode (cathode) reduction potential – the anode (anode) reduction potential

+0.34 – (- V 1.100 = (0.76

Or from the sum of the two oxidation potentials of the anode and the reduction potential of the cathode: oxidation potential of the anode (anode) + reduction potential of the cathode (cathode)

+0.34 + V 1.100 = 0.76

That is, the cell potential difference in the absence of an external current is 1.100 volts. This voltage is called the electromotive force.

Voltage difference when operating the battery[عدل]

The relationship between potential difference and electromotive force (emf).

Assume a battery E has an emf of E = 12 volts and an internal resistance of 2 ohms, connected to an external resistance of 6 ohms and a switch. The potential difference between the two terminals of the battery with the switch open (no current flowing):

12 volts = V = E

Potential difference when the switch is closed: We first determine the current intensity from the relationship:

Ampere (I= E ÷(R+r).

Where:

• E is the electromotive force of the battery
• R is the external resistance
• r is the internal resistance of the battery

So we get the current:

1.5 amps = (I= 12 ÷ (6 + 2)

Then we get the potential difference V:

V=EI.r

9 = (2 * 1.5) – 12 = V

Conventional direction of electric current[عدل]

An electric current flows through a conductor from the positive (cathode) to the negative (anode) electrode. This is what scientists have long ago agreed upon, because the discovery of electric current occurred before the discovery of electrons, so it was agreed upon.

Conventional direction: the direction of current in the external circuit from the positive pole to the negative pole of the battery.

Electronic direction: from the negative (electron-rich) to the positive (electron-poor) pole outside the battery.

Work done in electricity[عدل]

The work done is the work required to move an electrical quantity of 1 coulomb between two points that have a potential difference. Work is measured in joules, according to the relationship:

W = Q x V

Where:

W work joules

Q is the quantity of electricity in coulombs

V potential difference volts

From this relationship, voltage can be defined:

A volt is the potential difference between two points when 1 joule of work is required to transfer 1 coulomb of electricity from one point to the other.

1 joule = 1 coulomb x volt

• Note that the electrical energy unit is the joule, which is the same as the thermal energy unit. According to thermodynamics, all kinds of energy can be converted to each other.

See also[عدل]

• Galvanic corrosion
• Galvanization
• battery
• accumulator
• Zinc-carbon battery
• Lithium ion battery
• lead battery
• car battery
• Electrochemistry
• half reaction
• oxidizer
• List of standard efforts
• Electrochemical engineering

Reference[عدل]

• Electric gate
• Electronics portal
• Chemistry portal

In Commons, photos and files on: galvanic cell

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