Page 76 - Science Class 08

glaciers which leads to a rise in the sea level. dioxide which is extremely suffoca ng and
This may further cause floods in the coastal corrosive gas. On the other hand, on buring of
areas. It is believed that low lying coastal areas petrol, nitrogen oxides are released. When the
may even be permanently submerged under oxides of sulphur and nitrogen dissolve in rain
water. water, they form acid rain. It is very harmful for

crops, soil and monuments.

1. What kind of substances burn with a

flame?
2. What are the different colours and heat
zones of a flame?

3. What do you mean by the central zone of
a flame?
Acid Rain
4. What is the cause behind the global
On burning of fossil fuels, many oxides are
warming?
released. Coal and diesel releases sulphur

Combustion : Combustion is the process of burning of substances with the
evolution of heat and light

Ignition temperature : The lowest temperature at which a substance catches fire
Fire extinguisher : A device which is used to put out fire

Volatile substance : A substance which evaporates at normal temperature
Global warming : The rise in average temperature of the atmosphere of the earth due
to the increase in the amount of CO in the atmosphere
2
Acid rain : Rain drops which contain soluble acids like nitric acid

Let's R
Let's R
Let's Revise evise Let's Revise evise evise Let's Revise evise
Let's R
Let's R
I Antoine Lavoiseir first explained that fire was the result of a chemical reaction between a
burning substance and oxygen.
i Combustion is the process of burning of substances with the evolution of heat and light.

i When a substance does not burn completely, it is called incomplete combustion.
i Substances which catch fire easily and give a lot of heat are called combustible substances.
i Oxygen is the supporter of combustion.

i Due to incomplete combustion, carbon monoxide is released which is poisonous.
i The lowest temperature at which a substance catches fire is called its ignition temperature.

76 Science-8