Fire and Water
I was explaining to my neice the other day that a fire
requires oxygen in order to burn.
She asked the question: "If a fire requires oxygen atoms in order to burn
then how is it that water (which has 1 oxygen atom for each 2 hydrogen
atoms) will extinguish a fire"?
When something burns a spontaneous chemical reaction is occurring. When a
spontaneous reaction occurs energy is released and the products are more
than what you start out with. Water and carbon dioxide are the products of
combustion of most materials. The oxygen in water has already "burned" and is
no longer available to cause something else to burn.
When you put water on a fire it does two things. It displaces the free oxygen
molecules (which have two atoms of oxygen) so that it is not available to
participate in the burning process AND it turns to steam, carrying heat away
from the fire, cooling it to the point where it can no longer burn.
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Update: June 2012