ENERGY SOURCES

ENERGY SOURCES
Battery
A battery is an arrangement of several electrochemical cells connected in series that can be used as a source of direct electric current. They may be considered as store houses for electrical energy on demand. There are many types of electrochemical cells, including galvanic cells, fuel cells, electrolytic cells and voltaic cells.
In a battery, electrons from an electron – rich chemical (donor) flow through the external circuit and return to the battery in another chemical which is an electron acceptor. The flow of electron is called electron discharge. The difference between the two voltages of the donor – acceptor pair is the cell voltage.
A Cell contains only one anode and cathode.
A Battery Contains several anodes and cathodes.

Requirements of a useful battery
1. It should be light and compact for easy transport.
2. The voltage of the battery should not vary appreciably during its use.
3. It should have long life both when it is being used and when it is not used.

TYPES OF BATTERY
Batteries are broadly classified into the following categories:
i. Primary Battery (or) Primary cells (or) Non-reversible Battery

In these cells, the electrode and the electrode reactions cannot be reversed by passing an external electrical energy. The reactions occur only once and after use they become dead. Therefore, they are not chargeable and they have to be discarded after the exhaustion of their reactants.
Ex. Dry cell, mercury cell.

ii. Secondary Battery (or)Secondary cells (or) Reversible cells
In these cells, the electrode reactions can be reversed by passing an external electrical energy. Therefore, they can be recharged by passing electric current and used again and again. These are also called storage cells (or) Accumulators.
Ex. Lead acid storage cell, Nickel-cadmium cell.

iii. Flow Battery (or)Fuel cells
In these cells, the reactants, products and electrolytes are continuously passing through the cell. In this chemical energy gets converted into electrical energy.
Ex.ydrogen-oxygen fuel cell.

iv) Reserve Battery
In these batteries, the active metals are kept separated by special arrangement. When it has to be already used, an activation device makes it ready. Such a battery is designed for long storage before use.

ALKALINE BATTERY

ALKALINE BATTERY
It is an improved form of the dry cell. In this zinc act as anode and MnO2 act as cathode. The electrolyte in this cell is KOH (an alkali) and hence the name alkaline battery. This cell derives the power from the reduction of the cathode and the oxidation of the zinc anode.

Cell Reactions
At anode: Zn(s) + 2OH‾(aq) → Zn(OH)2(s) + 2e‾
At cathode: 2MnO2(s) + H2O(l) +2e‾ → Mn2O3 + 2OH‾(aq)

Overall Cell Reaction
Zn(s) +2MnO2(s) + H2O(l) → Zn(OH)2 (s) + Mn2O3 (s)

The emf of this cell is 1.5V. The zinc anode used in this cell is made porous to provide a large electrode area. This leads to the delivery of more current.
It sustains heavy use and has a longer shelf life. So it is called a heavy duty battery. It performs better in cold weather than the other type of batteries.

The main advantages of alkaline battery over dry battery are

(i) Zinc does not dissolve readily in a basic medium.
(ii) The life of alkaline battery is longer than the dry battery, because there is no corrosion on Zn. (iii) Alkaline battery maintains its voltage, as the current is drawn from it.

Uses:
It is used in calculators, watches.