Half-Cell and Cell Reactions

A reaction is a procedure in which one or more than one matter or reactants are transformed into one or more than one dissimilar or separate matter which are known as products. Reactions are divided according to our needs, the type of product we want, and the type of reactants we use for the reaction. A chemical reaction is a process that uses one or more than one reactant and changes them into totally different chemical substances or products. A chemical reaction changes the chemical properties that the reactants have. 

We are going to learn about electrolysis reactions. An electrolytic cell is used to change electrical energy into chemical energy and a half-cell is used in this reaction. The Daniell cell is also a type of electrochemical cell in which half-cell reaction and cell reaction takes place.

Electrochemical Cell

An electrochemical cell is a device which is usually used to produce electrical energy from the chemical reaction but it is also used to produce chemical reactions with the help of electrical energy. It generally works on redox reactions. There are two types of electrochemical cells present.

1. Galvanic cell/voltaic cell

This is a device that generates an electric current from energy which is released during the spontaneous redox reactions in two half-cells.

 Features

1. Redox: A chemical reaction which is reversible in nature in which one reaction is an oxidation and the other is a reduction, that is, reverse of oxidation.

2. Half-cell: Either of the two parts of an electrochemical cell which contains one electrode and one electrolyte.

2. Electrolytic cell

In electrolytic cells, electrolysis reactions take place in which electrical energy is induced by chemical reactions.

Features

1. An electrolysis reaction is the chemical change produced by passing an electric current through a conducting solution or a molten salt.

2. An electrolysis reaction can sometimes be thought of as running a non-spontaneous galvanic cell.

3. Electrodes of metal, graphite, and semiconductor material are widely used in electrolysis reactions.

4. The term ‘electrolytic’ means of, relating to, or using electrolysis.

Half-cell Reaction 

Each half-cell means that electrodes are placed in an electrolyte which separates both of the half-cells from each other. The separation is very necessary because oxidation and reduction don’t come in direct chemical contact which creates a potential difference. 

A half-cell reaction is either an oxidation or reduction reaction. In one, we lose electrons and in another, we gain electrons. These reactions take place in an electrochemical cell in which we lose electrons at anode where oxidation happens and gain at cathode where reduction happens.

A half-cell reaction is very useful or we can say functional in a galvanic or voltaic cell. We observe that electron flow occurs in the direction from anode to cathode through the medium of electrolyte to bring out electromotive force.

When half-cell reactions occur at any metal surface, they cause corrosion. In a half-cell reaction, both the donor of electrons as well as the acceptor of electrons must be present for the transfer of electrons to take place.

A galvanic cell or simple battery is made up of two electrodes and each electrode of the cell is known as half-cell, and the reaction that takes place at these electrodes individually is known as a half-cell reaction.

Cell Reaction 

Cell reaction describes the overall reaction of any electrochemical cell. Its reaction equation is an addition of the equation for two electrode reactions with the cancellation of electrodes. Cell reactions mainly work on the assumption that the right-hand electrode is cathode and the left-hand electrode is anode. That is by assuming that the spontaneous reaction is the one in which reduction is occurring in the right-hand compartment.

Cell Potential 

Cell potential is used to measure the potential difference between two half cells in an electrochemical cell. It happens because of the ability of electrons which can flow from one half-cell to the other. Cell potential is measured in voltage, which allows us to give a certain value to the potential.

Daniell Cell 

Daniell cell is a primary cell which has a constant electromotive force of about 1.1 volts as it electrodes like copper in a copper sulphate solution and zinc in dilute sulfuric acid or zinc sulphate, and these two substances are separated by a porous partition.

Conclusion 

Half-cell and full cell reactions, or we can say cell reactions, all take place in an electrochemical cell. It is a single arrangement of two electrodes and an electrolyte for producing electric current due to chemical action within the cell or producing chemical actions due to production of electricity. Salt bridge which is a U-shaped glass tube having a jelly-like inside is mixed with electrolyte and plays an important role in the smooth functioning of the cell. The electrochemical cell plays an important role in our day to day life as we use these cells in watches, decorations, etc. Voltaic cells are used for the generation of electrical energy, commonly known as batteries which are used in inverters, mobiles, etc.