MECHANISM OF FIRE

Why should we ignite to start the fire? Where do the blazing light and heat come from? An inquisitive mind always try to find the answers. Now we go..
We will consider a simplest combustion or burning reaction.
2H2 + O2 = 2H2O + heat
Here hydrogen combines with oxygen to form water and release heat. Suppose we ignite hydrogen gas in a jar, it reacts with atmospheric oxygen; burst into flames; forms water vapour; release of lot of heat and light energy. This reaction is still used in rockets.

BURNING LAID BARE:
Hydrogen molecule has two hydrogen atoms that are bonded together. So does the oxygen molecules. These bonds are weaker. If we supply little heat energy -igniting-the bonds break loose.

Now the loose atoms form a new molecule -water molecule (H2O). The bonds are stronger in this molecule.

Bonds are due to electrons. During the formation water molecule, electrons goes to lower energy levels. Hence their excess energy is released in the form of light and heat. That is flame and burning.
The released heat will sustain the combustion reaction. So the hydrogen will continue to burn with oxygen. That is igniting once is enough.

The burning is the oxidizing reaction or Redox reaction. It ultimately requires oxygen. The burning requires 1. fuel 2. oxygen 3. heat.
A fuel is normally hydrocarbons like petrol, oil, wood, methane. The oxygen is normally taken from the atmosphere on earth. But the rockets has to carry oxygen. First we have to supply little heat by lighting. Then the burning is self sustaining with the released heat.
There is the exhaust, which is normally carbon-di-oxide and water. We normally create heat energy in this way and we now worry about carbon-emission.
Our body burns food with oxygen we intake. We feel the heat energy released. Our body functions because of this energy. But our body do not emit light and turn into flames. But emits invisible infra-red light. As long as our body burns, we are alive.
ADVANCED:
Electron going from high energy to low energy means, "it spiral down to the low orbit". The electron is electrically charged (negative) particle. So when it goes in spirals, it will emit electromagnetic waves, So the physics says. The waves are in the form of visible or invisible light and heat.
When ever, the atoms forms new molecule or new bond like H2O, the electrons goes to low energy levels.
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