For Example Firefighters and the Chemistry of Combustion

Combustion is a fascinating reaction from the gentle light of a candle, to the comfort of the hearth, to the welcoming warmth of a campfire. But these are cases where combustion is controlled. In the cases of uncontrolled combustion, the fascination turns to fear, primal and pure. Thankfully, there are those who routinely face this fear to protect others from the danger. A brief consideration of combustion chemistry hints at the magnitude of their challenge. 

The primary combustion reaction is a straightforward redox reaction. A compound made primarily of hydrogen and carbon, a hydrocarbon, is usually the fuel. When hydrocarbons mix with oxygen, they can react to produce carbon dioxide (CO2) and water and heat. 

Hydrocarbon + oxygen — carbon dioxide + water + heat 

In the reaction, the carbon is oxidized (literally gaining oxygen this time) and the oxygen gas gains enough electrons to attract hydrogen and form water, so it is reduced. 

How do we know that it was COj that caused the change Take a clean glass and prepare another solution with four teaspoons water (20 milliliters) and two drops of fish-tank indictor. Now blow up a balloon. Holding the balloon pinched shut, put the balloon on one end of a straw and put the other end of the straw down into the indicator solution. When you ease open the neck of the balloon, freshly exhaled COj from your lungs will bubble quickly through the solution and you should see the indicator once more turn from green-blue to yellow. 

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