Worksheet solutions for chapter: Combustion and Flame for class 8 are provided below.
(1) What is spontaneous combustion?
Spontaneous combustion is a combustion in which a material suddenly burns without heating form outside. The heat required for the process is produced by slow oxidation of material. It happens at the room temperature. Spontaneous combustion takes place only in those materials which have very low ignition temperature.
(a) Phosphorus burns in air at room temperature.
(b) Coal dust has resulted in many disastrous fires in coal mines because of spontaneous combustion. Coal ignites spontaneously when exposed to oxygen and heats on its own if there is no ventilation for cooling.
(2) Why blanket wrapped around a person who got fire?
Wrapping of blanket around the burnt person cuts the supply of oxygen which is very necessary for burning. As the result of it fire stops at once.
(3) Is heat from the Sun an example of combustion?
Heat from the sun is not an example of combustion. Combustion is a chemical process in which a substance reacts with oxygen to gives off heat and sometimes gives off light either in the form of flame or glow. But, in the sun, heat and light are produced by nuclear reactions not by combustion.
(4) Cooking oil never catches fire when a frying pan is kept for long on a burning stove?
Cooking oil never catches fire when a frying pan is kept for long on a burning stove because heat supplied to frying pan is transferred to cooking oil by conduction. Thus, oil never reaches its ignition temperature and never catches fire.
(5) A person is throwing water on fire caught by oil. But he is not getting success to extinguish fire. Why?
Throwing of water will not work if fire is involving oil or petrol. Water is heavier than oil. Therefore, it sinks below the oil and oil keeps burning above.
(6) What is acid rain and why it is not useful?
Burning of coal and diesel releases Sulphur dioxide gas. 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. Such rains are called acid rains. It is very harmful for crops, buildings and soil.
(7) In an experiment 15000 kj/kg calorific value produced by 2 kg fuel. What is the amount of heat produced?
Calorific value = 15000kj/kg
Weight of fuel= 2kg
Calorific value = Heat Produced / Weight of the fuel
Heat produced = Calorific value weight of the fuel
= 15000 2
= 30000 kj
Hence, fuel produced 30000kj heat.
(8) What is inflammable substance?
The substances which have very low ignition temperature and can easily catch fire with a flame are called inflammable substances.
Eg:- Petrol, Liquified Petroleum Gas (LPG) etc.
(9) Fill in the blanks
(i) _____ and _____ are the best fire extinguishers.
(ii) Kerosene has _____Igneous temperature than wood.
(iii) Partially combustion takes place in _____ zone of flame.
(i) Water and carbon- dioxide are the best fire extinguishers.
(iii) Kerosene has low igneous temperature than wood.
(iii) Partially combustion takes place in luminous zone of flame.
(10) What is a flame? Name all three zone of the flame.
A hot burning gaseous part of the substance is called flame.
Eg:- wax, kerosene etc. provide flame when burns.
Three zones of flame are
(i) Dark zone
(ii) Luminous zone
(iii) Non – luminous zone