Skip to main content

CBSE NCERTCLASS 8TH COMBUSTION AND FLAME (self study notes)

A chemical process in which a substance reacts with oxygen to give off heat is called combustion.
The substance that undergoes combustion is said to be combustible.
The substances that do not burn on being exposed to flame are called  non-combustible  substances.
like stone, glass, iron nails, etc.
Ignition temperature:  The lowest temperature  at which a fuel catches fi re is called  its  ignition temperature.
Types of combustion : Combustion can be of different types.  It can be spontaneous, rapid, slow or incomplete.
Spontaneous combustion: combustion reaction that occurs without the help of any external heat is called
spontaneous combustion e.g. When white phosphorus is exposed to air at room temperature, it
catches fi re immediately; even without  being lit by a match stick
Rapid combustion : combustion reaction that occurs with the help of any external heat is called Rapid combustion e.g. Bursting of fire crackers, burning of camphor. Magnesium wire in air, gas in a burner and kerosene  in a stove
Slow combustion : Combustion that takes place at a very slow rate is called slow combustion.
During this type of combustion low heat and light are produced. Food oxidized  in our body to release energy is an example of slow combustion.
Glucose + Oxygen   ---------à Carbon dioxide + water + energy
Incomplete combustion : Combustion takes place in the presence of oxygen. If the supply of oxygen
is insufficient, then combustion will be incomplete. This is called incomplete combustion. Carbon forms carbon monoxide when it undergoes incomplete combustion.
                 Carbon +   Oxygen   -------à carbon monoxide
FIRE CONTROL
Fire can be controlled and extinguished by
1.  Removing any combustible materials near the region of fi re.
2.  Cutting off the supply of air by  using sand or blanket.
3.  Bringing down the ignition temperature by using water
Water should not be used for oil fire. Why?
 Oil being lighter, fl oats, spreads and causes severe damage. So, oil fi re should be extinguished by using substances called foamite.
How does fires caused by electrical appliances or installations extinguished?
Fires caused by electrical appliances or installations extinguished by using solid carbon dioxide
or carbon tetrachloride. The risk of electrical shock is too great, if water is used.
FLAME AND ITS STRUCTURE
Different parts of a candle fl ame

Zone of non-combustion: This is the dark zone that lies around the wick. It contains  un burnt gas particles. No combustion takes place here as no oxygen is available.
Zone of partial combustion: In this zone, the hydrocarbons present in the oil gas decompose
into free carbon and hydrogen. The un burnt carbon particles impart a pale yellow colour to the flame. This is the luminous part of the flame.
Zone of complete combustion (blue) : This is the non-luminous thin zone  of the flame. It is the outermost hottest region in the fl ame that is invisible. Here, carbon and hydrogen are completely oxidized to Carbondioxide and water vapour.
Carbon + Oxygen ------à  Carbon monoxide (blue flame)
Carbon monoxide + Oxygen---------à Carbon dioxide + Water (vapour)
Fuel: Any substance that can be burnt or otherwise consumed to produce heat energy is called a fuel. Wood, natural gas, petrol, kerosene, diesel, coal, and LPG are commonly used as fuels
Characteristics of a Good Fuel
1.  It should be cheap and readily available.
2. It should be easy to store, transport and handle.
3.  It should not produce toxic fumes or smoke or other harmful products on combustion.
4.  The amount of soot or ash left behind should be minimum.
5.  It should have a high calorific value.
6.  It should have a low ignition temperature.
Calorific Value: The amount of heat energy liberated when 1 kg of the fuel is burnt completely in oxygen is called the calorific value of the fuel.
Types of Fuels
There are three types of fuels. They are solid, liquid, and gaseous fuels
Solid Fuels
Coal, wood, charcoal, coke, and paraffin are some commonly used solid fuels.
The drawbacks of solid fuels are as follows:
1. They have a high ignition temperature.
2. They produce a large amount of residue (soot, ash) after combustion.
3. Their calorific value is low
Liquid Fuels : Petrol, kerosene, and diesel are some commonly used liquid fuels
which are obtained from petroleum (an oily mixture of hydrocarbons in its crude form). Ethyl alcohol is also a liquid fuel. Locomotives, buses, and lorries use diesel as the fuel.
Gaseous Fuels :Gases such as methane, carbon monoxide and hydrogen are combustible. Natural gas, producer gas, coal gas, water gas, LPG (liquefi ed petroleum gas), and biogas (gobar gas) are other examples of gaseous fuels

Why gaseous fuels do are referred over solid and liquid fuels?
.Gaseous fuels are preferred over solid and liquid fuels because of the following advantages.
•  They have a low ignition temperature.
•  They burn completely (complete combustion) and leave no residue (soot, ash, smoke).
•  They are easy and safe to handle, transport, and store.
• They have a high calorific value.
• They are cheap.

Harmful effects of burning of fuel on the environment.

1. Carbon fuels like wood, coal, petroleum release unburnt carbon particles. These fine particles are dangerous pollutants causing respiratory diseases such as asthma.
2. Incomplete combustion of these fuels gives carbon monoxide gas. It is a very poisonous gas. It is dangerous to burn coal in a closed room. Because the carbon monoxide gas produced can kill persons sleeping in that room.
3. Combustion of most fuels releases carbon dioxide in the environment. Increased concentration of carbon dioxide in the air is believed to cause global warming.
4. Burning of coal and diesel releases sulphur dioxide. It is an extremely suffocating
and corrosive gas. Moreover, petrol engines give off gaseous oxides of nitrogen. Oxides of sulphur and nitrogen dissolve in rain water and form acids

Comments

CBSE ADDA :By Jsunil Sir : Your Ultimate Destination for CBSE Exam Preparation and Academic Insights

Class 10 Chapter 02 Acid Bases and Salts NCERT Activity Explanation

NCERT Activity Chapter 02 Acid Bases and Salt Class 10 Chemistry Activity 2.1 Indicator Acid Base Red litmus No Change Blue Blue Litmus Red No change Phenolphthalein Colourless Pink Methyl Orange Pink   Yellow Indictors are substance which change colour in acidic or basic media. Activity 2.2 There are some substances whose odour changes in in acidic or basic media. These are called olfactory indicators. Like onion vanilla, onion and clove. These changes smell in basic solution. Activity 2.3 Take about 5 mL of dilute sulphuric acid in a test tube and add few pieces of zinc granules to it. => You will observe bubbles of hydrogen gas on the surface of zinc granules. Zn + H2SO4 --> ZnSO4 + H2 => Pass the Hydrogen gas through the soap solution. Bubbles formed in the soap solution as Hydrogen gas it does not get dissolved in it

Living science ratna sagar class 6 solutions

Ratna sagar living science 6 answers by jsunil. Class6 Living science solution Term-1 Living Science Solution chapter-1 Source of food Download File Living Science Solution chapter-2 Component of food Download File Living Science Solution chapter-3 Fibre to fabric Download File Living Science Sol ch-4 Sorting of material into group Download File Living Science Soln ch-5 Separation of substance Download File Living Science Solution chapter-6 Change around Us Download File Living Science Solution ch-7 Living and Non Living Download File Living Science Solution ch-8 Getting to Know Plants Download File Living Science Sol ch-9 The Body and Its movements Download File Visit given link for full answer Class6 Living science solution Term-II

Class 10 Metal and Non MetalsChapter 03 NCERT Activity Solutions

X Class 10 NCERT Activity Explanation Class 10 Metals and Non Metals Activity 3.1 Page No. 37 Take samples of iron, copper, aluminium and magnesium. Note the appearance of each sample. They have a shining surface. Clean the surface of each sample by rubbing them with sand paper and note their appearance again. They become more shiny. => Freshly cut Metal have shiny surface Activity 3.2 Page No. 37 Take small pieces of iron, copper, aluminium, and magnesium. Try to cut these metals with a sharp knife and note your observations. They are very hard to cut. Hold a piece of sodium metal with a pair of tongs and try to cut it with a knife. Sodium can be cut easily with knife. Hence K and Na are soft metal cut with knife Activity 3.3 Page No. 38 Take pieces of iron, zinc, lead and copper try to strike it four or five times with a hammer. These metals are beaten into thin sheet on hammering. This property of metal is called malleability and metals are called malleable. Activity 3.4 Page

CBSE I NCERT 10th Numerical Problem solved Reflection and reflection of light

Q. 1. A concave mirror of focal length 20cm is placed 50 cm from a wall. How far from the wall an object be placed to form its real image on the wall?  Solution: V= -50 cm F= -20cm From mirror formula 1/u = 1/f – 1/v = -1/20+ 1/50 = - 3/100  U = - 33.3 cm Therefore, the distance of the object from the wall x =  50 – u X = 50 – 33.3 = 16.7 cm. Q.2. An object is placed at a distance of 40cm from a concave mirror of focal length 15cm. If the object is displaced through a distance of 20 cm towards the mirror, By how much distance is the image displaced? Answer: Here f = - 15 cm, u = - 40 cm Now 1/f = 1/u + 1/v Then 1/v = 1/f – 1/u Or V= uf/u-f =( - 40 x -15)/25 = -24 cm Then object is displaced towards the mirror let u1 be the distance object from the Mirror in its new position. Then u1 = -(40-20) = -20cm If the image is formed at a distance u1 from the mirror then v1 = u1f/u1-f = -20X-15/-20+15 = -60 cm. = - 20 x-15/-20+15 = -60 cm. Therefor

Electricity numerical for class 10 CBSE Trend Setter 50 Problems

1. The current passing through a room heater has been halved. What will happen to the heat produced by it? 2. An electric iron of resistance 20 ohm draws a current of 5 amperes. Calculate the heat produced in 30 seconds. 3. An electric heater of resistance 8 ohm takes a current of 15 A from the mains supply line. Calculate the rate at which heat is developed in the heater. 4. A resistance of 40 ohms and one of 60 ohms are arranged in series across 220 volt supply. Find the heat in joules produced by this combination in half a minute. 5. A resistance of 25 ohm is connected to a 12 V battery. Calculate the heat energy in joules generated per minute. 6. 100 joules of heat is produced per second in a 4 ohm resistor. What is the potential difference across the resistor? 7. An electric iron is connected to the mains power supply of 220 V. When the electric iron is adjusted at minimum heating’ it consumes a power of 360 W but at ‘maximum heating’ it takes a power of 840 W. Ca