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Chemical Energy into Electrical Energy- Physics Guide for Class 8

Chemical Energy into Electrical Energy- Physics Guide for Class 8

Information about Chemical Energy into Electrical Energy

Title

Chemical Energy into Electrical Energy

Class

Class 8

Subject

Class 8 Physics

Topics Covered

  • Conversion of Chemical Energy into Electrical Energy
  • Chemical Effects of Electric Current
  • Anode
  • Cathode


Conversion of Chemical Energy into Electrical Energy

We know that it is possible to convert one form of energy into another; however, energy can neither be created nor destroyed. The list of 'conversions', of one form of energy into another, is almost endless. 
  • The electric cells give us electrical energy at the expense of chemical energy. 
  • We can, therefore, say that the cells are an example of conversion of chemical energy into electrical energy. 
  • It was an Italian scientist, Alessandro Volta, who gave us the first practical 'source of such a conversion' in the year 1790. His arrangement is known as the voltaic cell.

The general set-up of a voltaic cell is shown in the figure given below.
  1. When two rods of zinc and copper (known as electrodes) are dipped in a solution of dilute sulphuric acid, there are chemical reactions within the system.
  2. It is these reactions that help us to get electrical energy from chemical energy.
  3. When we connect its two rods, to a (torch) bulb/ LED, using metal wires, a current flows and the bulb/LED 'lights up'. 
  4. he voltaic cell can, therefore, act as a source of electric current or electrical energy.

Chemical Effects of Electric Current

We now realise that chemical changes in a liquid can produce electric effect (electric current). Is the reverse also possible? Can an electric current, passing through a liquid, result in chemical changes? 

  • Michael Faraday, a well-known British experimental physicist, began his experiments on the passage of electricity through liquids (electrolyte) in 1834.
  • He observed interesting chemical changes (effects) taking place when an electric current passes through an ionic solution. The resulting effects are known as chemical effects of current.
  • Faraday called the phenomenon, resulting from the passage of electricity through liquids, as electrolysis. This is because it causes chemical changes within the electrolyte. 

Let us now perform an activity to find out the kind of chemical effects (changes) that take place when an electric current passes through an ionic solution. 

Activity 1
To demonstrate the electrolysis of water.
Material required:
A battery of 9V (six cells of 1.5 V), two graphite pencils, a beaker, tap water, connecting wires and tape.
Procedure:
  • Sharpen both ends of both the pencils.
  • Fill the beaker with tap water.
  • Make a simple circuit as shown below.
  • It is important to make good contact with the graphite in the pencils.
  • Secure the wires with tape.
  • Use a piece of cardboard to hold the pencils in a vertical position.
  • Place the exposed tips of the pencils in the water, such that tips are fully submerged but are not touching the bottom. We are using the two pencils as the electrodes here. 
  • Now, wait for 3-4 minutes and observe the electrodes carefully.
Small gas bubbles are seen to be getting formed near the electrodes. 
Note: We can add a few drops of an acid/small amount of salt (with proper, and appropriate precautions), to make water more conducting.] 

It was a British Chemist, William Nicholson, who had shown that if electrodes were immersed in water and a steady current was passed through it, bubbles of oxygen and hydrogen are produced.

  • The oxygen bubbles are formed on the electrode (called anode) connected to the positive terminal of the battery and hydrogen bubbles are formed on the other electrode (called cathode) connected to the negative terminal of the battery.
We, thus, conclude that the passage of an electric current, through an ionic solution, can cause chemical changes.

The chemical reactions taking place in the solution depend on the:
  1. nature of the electrodes.
  2. nature and concentration of the solution.
Some of the prominent effects of the chemical reactions, taking place at electrodes and within the solution, are:
  1. Metals may get deposited at the electrode surface.
  2. Gaseous bubbles may get formed near the electrodes.
  3. Change of colour of solution may occur due to dissolution of different ions.

When an electric current passes through a pure metallic conductor, whether solid or liquid (e.g. mercury), there is no chemical effect, i.e. there is no change in the chemical composition of the conductor. There is only the usual heating effect of current. 

The phenomenon of electrolysis, i.e. passage of current through an ionic solution, is different from the conduction of electricity through metals in two important ways:
(i) Flow of current can cause chemical reactions.
(ii) Unlike conduction in metals matter, here, gets actually transported through the solutions. 
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