Comprehensive WBBSE Class 10 Physical Science Notes Chapter 1 Concerns About Our Environment can help students make connections between concepts.
Concerns About Our Environment Class 10 WBBSE Notes
Environment : It is defined as the sum total of physical and biological factors that directly influence the survival, growth, development and reproduction of organisms.
Environmental chemistry: The branch of chemistry which deals with the study of various chemical phenomena occuring in the environment is called, environmental chemistry.
Environmental components of earth : Earth’s environment is composed of the following components :
1. Atmosphere 2. Hydrosphere 3. Lithosphere 4. Biosphere Among these the first three components are abiotic while the fourth one is biotic.
1. Atmosphere: This comprises a blanket of gaseous layer that extends to a height of about 1600 km above the surface of earth.
The atmosphere has been divided into four distinct zones. These are :
- Troposphere
- Stratosphere
- Mesosphere
- Thermosphere.
Different regions of atmosphere
2. Hydrosphere: It includes all sources of water such as seas, oceans, lakes, rivers, fountains, polar regions, glaciers, ground water etc.
3. Lithosphere: It comparises of the solid crust of the earth, made up of rocks forming the outermineral cover. It includes soil, minerals, organic matters etc. and extends up to a depth of about 30 km from the earth’s surface.
4. Blosphere 3 It is that portion of the earth where living organisms exist and interact with one another and also with the non-living components.
Biosphere consists of all the three regions, e.g. soil, water, air etc. where living beings exist.
Temperature distribution with height above earth’s surfaces :
Ozone layer: In the lower region of the stratosphere (the region at the hieght of 15 km to 35 km from the ground) there exists a layer of ozone gas. This layer is called ozone layer or ozonosphere. Almost 90 % of total ozone gas exists in this layer.
Formation of ozone layer : O2(Oxygen molecule) present in the stratosphere absorbs UV (ultra violet) (λ = 255 nm ) radiation coming from the sum and decomposes to form oxygen atom (O). This atomic oxygen combines with oxygen molecule to form ozone molecule.
Formation of O2 from O3 ; Ozone molecules also absorbs UV-radiation and gets converted into oxygen molecule (O2)
Fixation of quantity of ozone in the stratosphere: In the ozone layer of the stratosphere, these two opposite process (i.e. formation of ozone molecule and the decomposition of ozone molecule) occur in a cyclic order and finally attains a state of equilibrium. Because of the existense of such an equilibrium state, quantify of ozone in the stratosphere remains fixed.
Role of ozone layer in the environment : Ozone layer absorbs most of the harmful UV-radiation emitted by the sun because this ray is utlised in the production and decomposition of ozone.
Harmful effect of UV-radiation:
- ultraviolet radiation causes cancer in human skin.
- damages the cornea of the eyes and develops premature cataract.
- In addition, immunity against diseases and fertility in living beings decreases.
Ozone hole (Depletion of Ozone layer); The phenomenon of thinning of the Ozone layer of the stratosphere is known as depletion of ozone layer or ozone hole.
In 1982, the British scientist Jo Foreman first observed ozone hole.
Causes of depletion of ozone layer or formation of ozone hole:; Due to the influx of several foreign substances into the atmosphere, the rate of decomposition of ozone has far exceeded than that of its formation. This has resulted in the thinning of ozone layer in the stratosphere almost everywhere.
The factors which accelerate the ozone depletion are as follows :
Some chemical substances belonging to the class of chlorofluorocarbons (Freons or CFC ) are mainly responsible for the formation of ozone hole.
| Name | Formula | Trade Name |
| Trichloro fluoro methane | CFCl3 | Freon-1 |
| Dichloro difluoro methane | CF2Cl2 | Freon-12 |
| Dichloro fluoro methane | CHCl2F | Freon-22 |
| Dichloro trifluoro ethane | CHCl2-CF3 | Freon-113 |
| Dichloro fluoro ethane | CH3-CCl2F | Freon-1146 |
Use of the above mentioned chemicals :
- refrigerants
- propellants in aerosols
- foaming agent in plastic production
- as solvents for various purposes.
A cyclic process continues, which eventually causes depletion of ozone layer.
It has been experimentally found that a single Cl atom is capable of decomposing millions of O3 molecules.
Halocarbons : It has been found experimentally that halons i.e. halocarbons which are generally used as fire extinguishers and as pesticides e.g. Halon-1301 i.e. bromo trifluoro methane (CF3 Br), Halon-1211 i.e. bromochloro difluoro methane (CF2BrCl). Halons are stable in the troposphere. But in the stratosphere, they absorb UV-radiation and decompose to produce active bromine atoms ( Bi). Thus produced active Br atoms convert ozone molecule of ozone layer to oxygen molecule and free radical bromine monoxide ( BrO ). They produced bromine monoxide (BrO) reacts with more ozone to give more oxygen and active Br atoms. In this way, the entire process proceeds continuously in a cyclic manner which lead to decay of the ozone layer.
Oxides of Nitrogen (NO, NO2) : The gaseous oxide of nitrogen is produced due to human activity or naturally in the troposphere. Major portion of this gas is produced in the exhaust gases of supersonic planes flying in the stratosphere and thus the gas is added directly into the stratosphere.
Here NO (Nitric oxide) gas comes in contact with the ozone and reacts to form NO2and O2. The NO thus reacts with Oxygen atoms and formed NO2due to the decomposition of ozone molecules by the UV-rays. Nitrogen dioxide (NO2) reacts with Oxygen atoms to produce back Nitric Oxide (NO) gas. This explains why the ozone molecules undergo continuous decomposition although the quantity of Nitric oxide (NO) is not diminised.
Green house: Green house is a large chamber made of glass on the soil. When the plants of tropical countries are taken to cold countries, they cannot adapt themselves to the climatic conditions of the cold countries.
Green house gases: These are some gases which are present in earth’s atmosphere e.g. carbon dioxide (CO2), methane (CH_4), water vapour (H2O), chlorofluoro Carbon (CFC), ozone (O3), nitrous oxide (N2O).
The green house gases form a layer surrounding the earth’s surface which act like that of the glass walls and roof of the green house and keep the atmosphere of earth’s surface warmer. These gases are known as green house gases.
Green house effect: The natural process by which a layer of green house gases present in the atomsphere surrounding the earth’s surface, instead of allowing the infrared radiation reflected by earth’s surface to pass out into the outer space, partly absorbs the radiated heat and reflects back the rest to the earth’s surface and thus keeps the surface of the earth and the adjacent atmosphere warm, which is suitable for the existence of the living beings, is known as green house effect.
Global warming : It has been observed that in the last few centuries the average temperature of the earth is gradually increasing. For example, during the period from 1800-1900 AD, the average increase of the earth’s temperature was found to be 0.4° C and during the period 1900-2000 AD this increase in temperature is 1° C. So it cannot be denied that the natural environment is gradually becoming warmer.
The phenomenon of gradual increase of temper all over the world is called global warming.
Causes for the increasing concentration of green house gases in the atmosphere :
- Huge amount of coal is burnt daily in the thermal power stations for the generation of electricity.
- Excessive use of nitrogenous fertilizers in agriculture is the cause of increasing amount of nitrous oxide and oxides of nitrogen in the atmosphere.
- Combustion of huge amount of petrol and diesel in the automobiles and forest fires are the causes for the increase of carbon dioxide in the atmosphere.
- Extensive use of coal, wood, LPG etc., as fuels for the cooking purpose and to meet the other needs of the growing population. In consequence of which high amount of carbon dioxide gas is being added to the atmosphere.
- Due to the increase of paddy field, marshy lands, waste organic matters, the amount of methane gas in the atmosphere is going on increasing.
Some preventive meacures to reduce emiseion of green hotuse gases;
- In order to decrease the amount of carbon dioxide in the atmosphere the use of fossil fuels e.g. wood, coal, petrol, diesel, kerosene, L.P.G. etc., should be reduced as far as possible.
- Afforestation must be encouraged so that more carbon dioxide are absorbed by plants.
- Use of chlorofluoro carbon (CFC) must be stopped totally.
- Deforestation must be totally stopped legally.
- Instead of using coal, electric energy can be produced by using solar energy, tidal energy, wind energy. Electricity may be produced by using nuclear energy and hydroelectricity.
The calorific value of a fuel : It is the quantity of heat produced by its combustion at constant pressure under hormal’ (standard) conditions (i.e. to 0°C and under a pressure of 76 cm Hg pressure).
Higher calorific values for some common fuels: Coke, oil, wood, hydrogen etc.
Necessity of conservation of fossile fuels :
Advantages of Fossils fuels
Easily available : Since these fossil fuels have been of such a great source of energy, more and more extractions are going on every day.
Produce large amount of Energy : Fossil fuels are easily combustible.
High Caloricfic value : All energy produced has some calorific value. The more the value, the more effective it is.
Stability : The fossil fuels are composed of the molecules of carbon and hydrogen. This makes them very stable.
Transportation : This industries need regular supply of fossil fuel like oil, gas and coal. The biggest advantage of using fossil fuels is that they can be easily stored and transported from one place to another.
Abundantly available : Though every effort is made to make the usage of alternative fuels popular, still fossil fuels are most common ones in use. This is because, these are very easily available.
Low cost : Fossil fuels are available all over the world and the methods to extract energy from them are also not that expensive.
Easy set up : Since they are widely available, the construction of fossil fuel power plant can take any where in the world as long as they get large quantities of fossil fuels to feed them.
Sources of energy :
Solar energy: Solar power harvests the energy of the sun through using collector panels to create conditions that can be turned into a kind of power. Large solar panel fields are often used in desert to gather enough power to charge small substations, and many homes use solar systems to provide for hot water, cooling and supplement their electricity.
Wind energy: Wind power is becoming more and more common. The new innovations that are allowing wind forms to appear are making them a more comman sight. By using large turbines to take available wind as the power to turn, the turbine can then turn a generator to produce electricity.
Geothermal Energy: It is the energy that is produced from beneath the earth. It is clean sustainable and environment friendly. High temperature are produced continuously inside the earth’s crust by the slow delay of radioactive particles. Hot rocks present below the earth heats up the water that produces steam. The steam is then captured that helps to move turbines. The rotating turbines then power the generators.
The biggest disavantage with geothermal energy is that it can only be produced at selected sites throughout the world. The largest group of geothermal power plants in the world is located at the Geysers, a geothermal field in california, united states.
Hydroyen Energy : Hydrogen is available with water (H2O) and is most common element available on earth. Water contains two-thirds of hydrogen and can be found in combination with other elements. Once it is separated, it can be used as a fuel for generating electricity.
Hydrogen is a tremendous source of energy and can be used as a source of fuel of power ships, vehicles, homes, industries and rockets. It is completely renewable, can be produced on demand and does not leave any toxic emissions in the atmosphere.
Tidal Energy : Tital energy uses rise and fall of tides to convert kinetic energy of incoming and outgoing tides into electric energy. The generation of energy through tidal power is mostly prevalent in coastal areas. Huge investment and limited availability of sites are few of the draw-backs of tidal energy. When there is increased height of water levels in the ocean, tides are produced which rush back and forth in the ocean. Tidal energy is one of the renewable source of energy and produce large energy even when the tides are at low speed.
Wave Energy : Wave energy is produced from the waves that are produced in the oceans. Wave energy is renewable, environment-friendly and causes no harm to atmosphere. It can be hardnessed along coastal regions of many countries and can help a country to reduce its dependance on foreign countries for fuel. Producing wave energy can damage marine ecosystem and can also be a source of disturbance to private and commercial vessels. It is highly dependent on wavelength and can also be source of visual and noise pollution.
Hydroelectric Energy: Many people are not aware about that most of the cities and towns in the world rely on hydropower. Every time you see a major dam, it is providing hydropower to an electrical station somewhere. The power of water is used to turn generatots to produce the electricity that is then used. The problems faced with hydropower right now have to do with against of the dams.
Biomass Energy: It is produced from organic material and is commonly used throughout the world chlorophyll present in plants captures the Sun’s energy by converting carbon dioxide from the air and water from the ground into carbohydrates through the process of photosynthesis. When the plants are burned, the water and carbon dioxide is again released back into the atmosphere. Biomass generally include crops, plants, trees, yard clippings, wood chips and animal wastes. Biomass energy is used for heating and cooking in homes and a fuel in industrial production. This type of energy produces large amount of CO2into the atmosphere.
Nuclear Power: While nuclear power remains a great subject of debate as to how safe it is to use and whether or not it is really energy efficient when you take into account the waste it produces – the fact is it remains one of the major renewable source of energy available to the world. The energy is created through specific nuclear reaction, which is then collected and used to power generators. While almost every country has nuclear generators, there are moratorium on their use or construction as scientists try to resolve safely and disposal issues for waste.
Fossil Fuels (Coal, Oil and Natural Gas): When most people talk about the different sources of energy they list natural gas, coal and oil as the options – these are all considered to be just one source of energy from fossil fuels.