Saturday, July 18, 2009

No Batteries, No Life~!

I guess many of you will agree with me right? Nowadays, almost everyone rely on electrical appliances everyday. Imagine, what you'll be doing if battery was not invented? And do you know chemistry is the driving force behind the magics of batteries?

Firstly, let's see what's a battery.

In electronics, a battery or voltaic cell is a combination of many electrochemical Galvanic cells of identical type to store chemical energy and to deliver higher voltage or higher current than with single cells. There are many types of batteries, such as carbon-zinc batteries, lead acid-batteries, alkaline cells and others.
In this post, I'll talk more about carbon-zinc battery, since it's the most common and least expensive type of battery. Carbon-zinc cell is also known as Lechlanche's cell. It is a type of dry cell and is described as primary cell, because it cannot be recharged after used up.

Let's have a look at the cross-section diagram of a carbon-zinc cell.
Now, do you know how a battery produces electricity when connected in a circuit?

If you look at a battery, it will have two ends, a positive terminal and a negative terminal. If you connect the two terminals with wire, a circuit is formed. Electrons will flow through the wire and a current of electricity is produced. Inside the battery, a reaction between the chemicals takes place. But reaction takes place only if there is a flow of electrons.

How the reaction works?
The reaction inside battery is closely related to the oxidation and reduction in chemistry studies. The container of the carbon-zinc battery is a zinc case. Inside the case contains a layer of NH4Cl with ZnCl2 aqueous paste separated by a paper layer from a mixture of powdered carbon and manganese(IV) oxide(MnO2), packed around a carbon rod.

The outer zinc container of a dry cell is the negative terminal. So, the zinc is oxidised, the half equation is as below.
Zn(s) → Zn2+(aq) + 2 e-

Refer to the cross-section diagram, the carbon rod surrounded by a powder containing manganese(IV) oxide is the positive terminal. In the following reaction, The manganese dioxide is mixed with carbon powder to increase the conductivity.
2MnO2(s) + H2(g)→ Mn2O3(s) + H2O(l)
Note: The H2 comes from NH4+(aq) => 2NH4+(aq) + 2 e- → H2(g) + 2NH3(aq)

The NH3 combines with the Zn2+ and manganese is reduced from an oxidation state of (+4) to (+3). Hence the overall reaction happens in a carbon-zinc battery is:

Zn(s) + 2MnO2(s) + 2NH4+(aq) → Mn2O3(s) + Zn(NH3)22+(aq) + H2O(l)
I bet you've learn something about battery after sacrificing so much patience to read this post. Congratulation! No choice, chemistry battery is boring. =P
Lastly, even though batteries can bring us so much benefits and convenience, it is still recommended to avoid the excessive usage of electricity, to save the Earth!


  1. I used it for is the occasional mobile phone call, or for that dreaded "calling a tow truck on a rainy night" bit. Funny thing, though, even though I drive decade-old cars, I haven't needed a tow truck in over 20 years - except when I was in a wreck, and even then the Police called the tow truck, not me. batteroo

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