COMBUSTION & FLAME ncert_CLASS8

COMBUSTION : 

• a chemical process in which substance reacts with oxygen to give off heat is called as combustion 

• The substance that undergoes combustion called as fuel 

• The lowest Temperature at which the substances catches fire is called its IGNITION TEMPERATURE 

• Substances which have very low Ignition Temperature and easily catch fire with a flame are called Inflammable substances 

• Eg : Petrol , alcohol , LPG 

CALORIFIC VALUE : 

• The amount of heat energy produced on complete combustion of 1 kg of a fuel is called its calorific value . 

• The calorific value of a fuel is expressed in a unit called kilo joule per kg (KJ/Kg) 

CAUSES OF ACID RAIN : 

• Due to heavy pollution when oxides of sulfur and nitrogen dissolve in rain water and form acids such rain is called as Acid Rain

COAL & PETROLEUM ncert_CLASS8

• Coal is processed in industry to get some products such as COKE , COAL , TAR & COAL GAS 

• COKE : it is tough , porous & black . And almost a pure form of carbon . coke is used in manufacture of steel and in the extraction of many metals . 

• COAL TAR : it is black , thick liquid with an unpleasant smell . it is mixture of about 200 substances 

• These days , BITUMEN a petroleum product is used in place of coal Tar for metaling the roads .

• COAL GAS : obtained during the processing of coal to get coke 
  

PETROLEUM : it is a source to obtained petrol and diesel . 

• Petroleum is also called as BLACK GOLD 

NATURAL GAS :

•  Natural is gas is stored under high pressure in compressed form (CNG) . It is less polluting . It is a clear Fuel 

• In our country Natural Gas has been found in Tripura , Rajasthan , Maharashtra & in the Krishna Godavari Delta .

MATERIALS : METALS & NON METALS ncert_class8

• MALLEABILITY : The property of metal by which they can be beaten into thin sheets 

• DUCTILITY : The property of metal by which it can be drawn into wires is called ductility 

• METALS are SONOROUS , since they produce ringing sound when struck hard 
  

EXCEPTIONS : 

• SODIUM & POTASSIUM are soft and can be cut with a knife 

MERCURY is the only metal which is found in liquid state at room temperature 
SODIUM Metal is very reactive ,it reacts vigorously with oxygen and water . A lot of heat is generated in the reaction .It is therefore stored in KEROSENE .

SYNTHETIC FIBERS & POLYMER ncert_class8

·       POLYMER : the chain of small units of chemical substances

·       Cotton is also polymer called as cellulose . cellulose is made up of large number of glucose units

• TYPES OF SYNTHETIC OR MAN MADE FIBERS- Rayon , Nylon , Polyester & and acrylic 

• ·       THERMO-PLASTIC : plastics which get easily deformed on heating

        Eg : Polythene and PVC

• ·       THERMO-SETTING : doesn’t get moulded on heating

        Eg: Bakelite and Melamine

• ·       Bakelite is used for making electrical switches and handles for various for utensils

• ·       Melamine can resist fire and tolerate heat better than other plastics

• ·  TEFLON is a special plastic on which oil and water do not sticks . It is used for non stick coating on cookwares   

 

MICRO-ORGANISMS : FRIENDS or FOE ncert_class8

•Micro organisms are classified into Four Major Groups 

  i.e BACTERIA ,FUNGI, PROTOZOA , ALGAE 

•Viruses are also microscopic

•Algae and Fungi comes under multicellular microscopic organisms

 and they can survive under all type of Environment 

•Friendly micro-organisms used to make Curd ,bread and cake and 

alcohol also 

 

•BACTERIUM LACTOBACILLUS used to make Curd

•Mainly bacteria are used for : Preparation of medicines , to

 increase soil fertility, food etc

 

•Yeast is generally used in baking industry for making bread ,

pastries and cakes as they produce carbon dioxide during 

respiration and thus bubbles of the gas fill the dough  and increase

 its volume

•Some bacteria and blue green algae are able to fix Nitrogen from the atmosphere to enrich soil with nitrogen and increase its fertility . These microbes are commonly called Biological Nitrogen Fixer. 

 • Disease causing micro-organisms are called Pathogens. •Anopheles Mosquito carries parasite of Malaria .  
•Aedes Mosquito acts as a carrier of Dengue Virus  

•What is PASTEURIZATION ??  

 it is the partial sterilization of a product such as milk or wine

to make it safe for consumption and improve its keeping 

quality . It reduces the risk of food poisoning .   

WATER ncert_CLASS7

• SALINITY : 

  It is The amount of salt present in 1000grams of water .
  Average salinity of ocean is 35 parts per 1000 grams  
  DEAD SEA in ISRAEL have 340 grams per litre of water 

  • OCEAN CURRENTS : 

    It is the stream of water flowing constantly on the ocean surface in definite directions
    LABRADOR Ocean Current is cold current 
    GULF STREAM is a warm current 
    Areas where cold and warm currents meet experiances Foggy weather 

  • WAVES : 

    Rise and Fall of ocean water 
    

    TIDES :

     Rhythmic rise and fall of ocean water that too twice a day 
    

    TYPES OF TIDES : 

     1.SPRING TIDES : occurs when sun moon and earth comes in a single line. also called as High hides
    2. NEAP TIDES : occurs when Sun and Moon are in Right angle to each other i,e earth will be quarter to the sun and moon , because of that water on the surface of ocean rises up diagonally due to gravity of the sun and moon. Neap tides are also called as low tides
    

       

AIR ncert_CLASS7

• AIR is consist of :

• OXYGEN-21%
• NITROGEN-78%
• CO2-0.03%
• ARGON-0.93% 
• OTHERS-0.04%

• LAYERS OF ATMOSPHERE : 

  • TROPOSPHERE -13km 
  • STRATOSPHERE-50km contains OZONE layer in it
  • MESOSPHERE-80 KM Meteorites burn up in this air 
  • THERMOSPHERE -80-400 km helps in Radio Transmission 
  • EXOSPHERE - >400 km -contains Helium & Hydrogen 
    

  INSOLATION :  

  • Incoming solar energy intercepted by the Earth .The amount insolation decreases from EQUATOR towards POLE ,therefore temperature decreases from same manner  ,That is the reason Poles are covered with the SNOW 
  • Low temperature area is associated with cloudy skies and weather 
  • High pressure Areas are associated with clear and sunny skies 
  • AIR always moves from high pressure area to low pressure area