When a candle is burned: 1. The wax melts from the heat of the match and is absorbed by the wick. 2. The molten wax turns to vapor which burns and provides the flame. 3. The chemical reactions of carbon and hydrogen in the wax with oxygen produce carbon dioxide, water, and release energy in the form of heat and light.

2. What happens to the wax when
a candle is burnt???
 Wax melts when a
burning matchstick is
brought near it.
 The molten wax is
absorbed by the wick.
 The molten wax forms
wax vapours on
heating.
 The vapours of wax
burn during the
burning of candle.

3. BLOW out the candle and see
MAGIC….
 When we blow off one candle it
automatically catches the flame
from the burning candle next to
it.
 It is because the vapours from
wick are present near the
atmosphere of the wick.
 Carbon(C) + Oxygen(O₂) 
Carbon Dioxide(CO₂)
 Hydrogen(H₂) + Oxygen(O₂)
Water(H₂O)

4. What happens when a Fossil
fuel Is burnt???
Methane(Natural Gas)+ Oxygen  Carbon Dioxide +Water
Butane(LPG) + Oxygen  Carbon Dioxide + Water

5. What is Combustion???
 A chemical process in which a
substance reacts with oxygen to
produce oxides and release energy is
called .
 The substance undergoing combustion
is called .
 The energy produced during combustion
is usually in the form of heat and light,
sometimes sound is also given out.

6. Types of
Combustion
Depending on the speed of reaction:
 Rapid Combustion— takes place very fast
 Slow Combustion--- takes place very slow
 Complete Combustion—takes place in
excess of oxygen/air
 Incomplete Combustion—takes place in
absence of oxygen/air

7. Ignition Temperature
 When the cloths of a person catch fire,
the person is covered with a blanket to
extinguish fire.
 The lowest temperature at which a
substance catches fire is called its
ignition temperature.

8. Necessary Condition
For Combustion!!!
 Presence of a combustible substance
 Presence of a supporter of combustion
 Attainment of Ignition temperature

9. Extinguishing Fire…
 Removal Of the Combustible Substance
 Removal Of the supported of Combustion
 By lowering down temperature

10. What is FLAME???
 A flame is the visible (light-emitting),
gaseous part of a fire.
 It is caused by a highly exothermic
reaction taking place in a zone.

11. Different Zones of Candle Flame
 Zone of Complete
Combustion
 Zone of Incomplete
Combustion
 Zone of No Combustion

12. BEST FUEL…
• Fairly cheap and easily available
• Moderate ignition temperature
• Easy to store
• Should not cause pollution on burning
• Should produce a large amount of heat
energy for less amount burnt

13. Harmful Effects Of Burning
Fuels
 Leads to global warming due to release
of carbon dioxide
 Coal burning release sulphur dioxide
which form acid rain
 Incomplete combustion of fuels releases
carbon monoxide gas which is very
poisonous