Chapter: Chemistry - Energy Sources

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Energy Sources

1 Introduction 2 Nuclear Energy 2.1 Nuclear Fission 2.2 Nuclear fusion 2.3 Nuclear chain reaction 3 Nuclear reactor 3.1 Light water Nuclear Reactor 3.2 Breeder Reactor 4 Solar Energy 4.1 Solar energy conversion 4.2 Solar cell 4.3 Application of Solar Cells 5 Wind Energy 5.1 Wind Mill 6 Batteries 6.1 Types of batteries 6.2 Alkaline Battery 6.3 Lead Storage Battery 6.4 Nickel-Cadmium Battery 6.5 Lithium Battery 7 Fuel Cells 7.1 Hydrogen Oxygen Fuel Cell 8. Glossary

ENERGY SOURCES

 

1 Introduction

2 Nuclear Energy

2.1 Nuclear Fission

2.2 Nuclear fusion

2.3 Nuclear chain reaction

3 Nuclear reactor

3.1 Light water Nuclear Reactor

3.2 Breeder Reactor

4 Solar Energy

4.1 Solar energy conversion

4.2 Solar cell

4.3 Application of Solar Cells

5 Wind Energy

5.1 Wind Mill

6 Batteries

6.1 Types of batteries

6.2 Alkaline Battery

6.3 Lead Storage Battery

6.4 Nickel-Cadmium Battery

6.5 Lithium Battery

7 Fuel Cells

7.1 Hydrogen Oxygen Fuel Cell

8. Glossary

 

 

1 INTRODUCTION

 

Sufficient sources of energy are necessary for industrialized nations. Energy is used for heating, cooking, transportation and manufacturing. Energy sources can be generally classified as conventional and non-conventional. Over 85% of the energy used in the world is from conventional sources such as fossil fuels (coal and oil) and nuclear power.

 

The convenrtional energy sources depend on coal and oil. The burnt fuels result in the release of CO2 and other gases into the atmosphere causing environmental damage. There are abundant renewable sources of energy such as wind, sun, water, and biomass. These sources are pollution ofree and known as “ green energy “.

 

 

2 Nuclear Energy :

 

The enormous energy thus released during the Nuclear Fission & Fusion reaction is known as Nuclear Energy.

 

2.1 N uclear fission: It is the nuclear reaction in which heavy isotopes are split into lighter nuclei on bombardment by neutrons. Fission reaction of U235 is given below

 

2.2 Nuclear fusion:

 Process of combination of lighter nuclei into heavier nucleus with simultaneous liberation of largeamount of energy. (e.g) solar system


Nuclear fusion reaction occurs in sun.

 

2.3 Nuclear chain reaction:

 


 

 


Differences between fission and fusion reaction


 

Nuclear fission

1 It is a process of breaking at heavier nucleous.

2 It emits radioactive rays

3 The mass number and atomic number of new elements are lower than

4 It occurs at ordinary temperature

5 It gives rise to chain reaction

6 It emits neutrons

7 It can be controlled

 

 Nuclear fusion

1. It is a process of combination of lighter nuclei.

2. It does not emit any kind of radioactive rays

3. The mass number and atomic number of product is higher than that of starting elements

4. It occurs at high Temperature

5. It does not give rise to chain reaction

6. It emits positrons

7. It canot be controlled

 

3 Nuclear Reactor

 

3.1 Light water nuclear power plant Definition

 

Light water nuclear power plant is one in which U235 feed rods are submerged in water.

 

Here the water acts as coolant and moderator.

 

The fission reaction is controlled by inserting or removing the control rods of B10 automatically from the spaces I between the fuel rods.

 

The heat emitted by U235 absorbed by the coolant in the fuel core is Heat is transferred to sea water and then converted into steam. The steam then drives the turbines, generating electricity.


(Structure of light water nuclear power plant)

 

3.2 Breeder reactor

 

A nuclear reactor with conversion or multiplication factor greater than one is a breeder reactor. A

 

breeder reactor generates fissionable nuclei from fertile nuclei. E.g., the fertile material like uranium-238 is converted into fissile 94 Pu239 by using slow neutrons. 94 Pu239 undergoes fission and produces energy.


 

Working :

`In breeder reactor, 92U235 is used as trigger to produce sufficient neutrons. These are used to convert 92U235 to Plutonium undergoes fission with the production of three neutrons. One neutron is used to propagate fission chain. The other two neutrons react with 92U238                                        to fissionable 94Pu239. Thus breeder reactor produces two 239    Pu atoms for each 238 U consumed. Thus more fissionable material is produced than consumed. Hence the reactor is called breeder reactor.

 

Critical Mass:

 

The minimum amount of fissile material (U235) required to continue the nuclear chain reaction is called critical mass.

 

 

4 Solar Energy

Solar energy

 

The energy that derive directly from sunlight and can be converted into more useful forms is known as Solar energy.

 

4.1 Solar Energy Conversion

The energy conversion my occur iterms of heat & current.


4.2 Photo galvanic cell or Solar cell

PRINCIPLE:

 

The principle of Solar cell is based on photovoltaic effect. When light radiation falls on the p-n junction semi conductor device, charge separation takes place and a potential difference is setup. This causes flow of electrons and produces electricity.

 

Working:

 

When sun rays all on the top layer of p- type semiconductor, electrons from valence band are promoted to conductance band and cross the p-n junction into the n-type semiconductor. A potential difference is set up between the two layers. This causes flow of electrons and produces electricity. When the „p and „n layers are connected to an external circuit, electrons flow from „n layer to „p layer and current is generated.

 

 

4.3 Application of Solar Cell 

1. Lighting purpose

 

Now a days electrical street lights are substituted by solar street lights.

 


2. Solar pumps are run by solar battery

 

A large number of solar cells are connected in series to form a solar battery. Solar battery produces enough electricity to run water pump, etc., They are also used in remote areas where conventional electricity is not available.

 

SOLAR BATTERY


 

        Solar cells are used in calculators, electronic watches etc.

 

Solar cells are superior to other type of cells, because they are non-polluting and eco-friendly.

        Solar cells are used to drive vehicles.

 

        Silicon solar cells are used as a source of electricity in space crafts and satellites.

 

 

Advantages of Solar cells

 

        Solar cells are used in remote areas, forests and hilly regions.

        Maintenance cost is minimum.

        Solar cells are pollution free.

        They have long life.

 

Disadvantages

 

      Solar cells are costly.

 

      Storage of energy is not possible with solar cells.

 

 

5 WIND ENERGY

 

Moving air is called wind. Energy recovered from the forces of wind is called wind energy.

 

5.1 Generation of electricity from wind mill

 

Wind energy is used to generate electricity with the help of wind mills. The crank of the wind mill is connected to a dynamo. When the blades of wind mill rotate, they turn the coil of the dynamo and produce electricity. Usually a number of wind mills are erected side-by-side. The outputs from the wind mills are coupled to generate electricity for commercial purpose. This type of system is wind energy farms.

 

Condition: Wind speed should be more than 15km/hr.

 

Advantages of wind energy

 

(i) It is cheap and economical. (ii) It is renewable

 

(iii) It does not cause pollution.

 

Disadvantages

 

        They produce noise.

 

Wind farms erected on the migratory routes of birds create problems. (iii) Wind turbines interfere with electromagnetic signals.

 

 

6 BATTERIES (or) ENERGY STORAGE DEVICES

Battery:

It is an arrangement of several electrochemical cells connected in series that can be used as a source of direct electric current.


 

6.1 TYPES OF BATTERIES

Secondary battery or secondary cells

 

In these cells, the electrode reactions can be reversed by passing an external energy.

 

They can be recharged by passing electric current.

 

They are called storage cells or accumulators.

 

Ex: Lead acid storage cell, Nickel- cadmium cell.

 

6.2 Alkaline Battery

 

Here the powdered zinc is mixed with KOH and MnO2 to get a gel. A Carbon rod acts as cathode. IT is immersed in KOH The outside cylindrical body is made up of zinc.

 

Cell reactions

 


Uses: It is used in calculators, watches etc., 


 

6.3 Lead storage cell Description:

 

 

It consists of number of voltaic cells connected in series Pb is anode and PbO2 is cathode

 

Number of Pb plates and PbO2 plates are connected in parallel.

 

Plates are separated from adjacent ones by insulators like rubber or glass fiber.

This arrangement is immersed in dil. H2SO4

Cell reactions


 

Overall reaction:

 

Pb (s) + PbO2(s) +                         2H2SO4 → PbSO4   + H2O + energy

 

Uses:

 

It is used to supply current mainly in automobiles such as cars. Buses, trucks, etc.,

 

* It is also used in gas engine ignition, telephone exchanges, hospitals, power stations.

 

 

6.4 Nickel – Cadmium Battery

Description

 

It consists of a cadmium anode. A metal grid containing a paste of NiO2 acting as a cathode. KOH is electrolyte

Ni-Cd battery


 

Cell reactions

 

 

Overall reaction:

Cd(s)  + NiO2 + 2H2O(l) → Cd(OH)2(s) + Ni(OH)2 (s) + energy

Uses: It is used in calculators. Electronic flash units, transistors and cordless appliances.

 

6.5 Lithium Battery

 

Description

 

It consists of a lithium anode and a TiS2 cathode.

 

A solid electrolyte generally a polymer is packed in between the electrodes.

 

The electrolyte permits the passage of ions but not electrons.

Cell reactions


Other types of secondary lithium batteries

 

            Li/ MnO2

 

                  Li/V2O5

                        Li/MoO2

                        Li/Cr3O8

 

Advantages of Li battery

 

It is the cell future. Why?

 

Its cell voltage is high, 3.0VSince Li is a light weight metal, only 7kg material required to produce 1mole of electrons.Since all the constituents of the battery are solids, there is no risk of leakage from the battery. This battery can be made in a variety of shapes and sizes.

 

Disadvantages of Li battery

 

Li battery is more expensive than other batteries

 

Uses

 

Button sized batteries are used in calculators, watches, cameras, mobile phones, laptop computers.

 

Lithium Battery

 

It is a solid state battery. Solid electrolyte is used.

 

Construction

 

It has a lithium anode and a TiS2 cathode. A solid electrolyte, a polymer, is packed in between the electrodes. The polymer electrolyte permits the passage of ions but not that of electrons.

 

Working (Discharging)

 

The anode is connected to cathode through the polymer electrolyte. Lithium ions and electrons are produced at the anode . The cathode receives the lithium ions and electrons.


Overall reaction: Li(s) + TiS2(s) --  --- > Li+ + TiS2- LiTiS2

Recharging

 

The battery is recharged by passing an external current, which drives the lithium ions back to the anode. The overall reaction is

LiTiS2  Li+ + TiS2

This cell has a voltage of 3.oV.

 

 

Uses:

 

It possesses very small size and high energy density. So it is used in calcutors, electronic flash units, computers, transistors head phones etc.

 

Advantages

 

         The cell has a voltage of 3.0V.

 

    Li is a light-weight metal. Just 7g (1 mole) of Li is required to produce 1 mole of electrons.

 

         Li has the most negative Eo value. So it gives a higher voltage than other cells. (iv)

 

It is a total solid state battery. There is no risk of current leakage from the battery. (v) It is manufactured in a variety of sizes and shapes.

 

Disadvantages

 

It is more expensive than other batteries.

 

 

7 FUEL CELLS:

 

Definition

 

Fuel cell is a voltaic cell. It converts chemical energy of the fuels directly into electricity without combustion. In these cells, the reactants and electrolytes are continuously

 

supplied to the cell.

 

Fuel + Oxygen -- -- > Oxidation products + Electricity.

 

Examples : Hydrogen - oxygen fuel cell.

 

 

7.1 Hydrogen - oxygen fuel cell

 

It is the simplest and most successful fuel cell. The fuel-hydrogen and the oxidiser-oxygen and the liquid electrolyte are continuously supplied to the cell.

 

Description

 

The cell has two porous electrodes, anode and cathode. The electrodes are made of compressed carbon containing a small amount of catalyst (Pt, Pd, Ag). Between the two electrodes an electrolytic solution, 25% KOH is filled

 

Working

 

Hydrogen passes through the anode compartment, where it is oxidised. Oxygen passes through the cathode compar tment, where it is reduced.


 

 

Advantages of Fuel Cells

        They are efficient and instant in operation.

        They are pollution free.

        They produce electric current directly from the reaction of a fuel and an oxidiser.

        They are light in weight

 

Disadvantages

        Fuel cells cannot store electric energy.

        Electrodes are expensive and short lived.

 

        H2 should be pure.

 

Applications

 

        H2 - O2 fuel cells are used in space crafts, submarines to get electricity

 

        In H2 - O2 fuel cell, the produt water is a valuable source of fresh water for astronauts

 

 

 

 

 

 

8 Glossary

Nuclear fission

 

The process of splitting of heavier nucleus into two or more smaller nuclei with simultaneous liberation of large amount of energy is called Nuclear Fission.

 

Nuclear Fusion

 

The process of combination of lighter nuclei into heavier nuclei, with simultaneous liberation of large amount of energy is called Nuclear Fusion.

 

Nuclear Chain Reaction

 

A fission reaction, where the neutrons from the previous step continues to propagate and repeat the reaction is called Nuclear Chain Reaction.

Breeder reactor

Breeder reactor is the one which converts non-fissionable material ( U238, Th232) into fissionable material ( U235, Pu239 ). Thus the reactor produces or breeds more fissionable material than it consumes.

Fissionable nucleides (or ) Fissile nucleides

 

The nucleides like U235, Pu239 which undergo fission reaction is known as Fissle nucleides.

Non- fissionable nucleides (or) Fertile nucleides

The nucleides like U238, Th232  which do not undergo fission reaction is known as

Fertile nucleides.

 

Critical Mass:

 

The minimum amount of fissile material (U235) required to continue the nuclear chain reaction is called critical mass.

 

Solar energy

 

The energy that derive directly from sunlight and can be converted into more useful forms is known as Solar energy.

 

Photogalvanic cell

 

Photogalvanic cell is one, which converts the solar energy (energy obtained from the sun ) directly into electrical energy.

 

Wind energy

 

Moving air is called wind. The energy possessed by wind is because of its high speed. The wind energy is harnessed by making use of wind mills, sky sail, ladder mill, kite ship etc.

 

Fuel cell

 

Fuel cell is a voltaic cell which converts the chemical energy directly into electricity without combustion. In these cells, the reactants, products and the electrolytes pass through the cell.

 

Battery

 

Battery is an arrangement of several electrochemical cells connected in series that can be used as a sources of direct electric current.

 

Electrolytic Cell

 

Electrolytic Cell converts electrical energy into chemical energy. Eg. Decomposition of water into hydrogen and hydroxide ion.

 

Electrochemical Cell

 

Electrochemical Cell converts chemical energy into electrical energy. Eg. Galvanic (or) Voltaic cell.


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