quimica das coisas


To know the chemistry of things is the first step to understand and to be able to act on the world around us. To demonstrate this, today we let talk about fire!

Fire, or rather, combustion, is actually an oxidation – reduction chemical reaction with great energy release. And why is it important to know this?  First of all, to fight a fire!

As with any other chemical reaction, fire exists only in the presence of reagents, which in this case are fuel (inflammable materials) and a combustive agent (which is usually oxygen from the air).

And, as in many chemical reactions, fire occurs only if the reagents are at an elevated temperature. Therefore, fire breaks out when combustible material are heated to their ignition temperature in the presence of a combustive agent. After the combustion reaction starts, it generates the heat needed to heat up more combustible material and fire spreads.

However, we just need to remove one of the essential components – fuel, combustible material or heat source – and the chemical reaction of combustion ceases. That is, the fire goes out!

Why is water so effective in fighting fire? Because it decreases fuel temperature, therefore stopping the reaction.

Another way to fight fire is to deprive it of one of the reactants. For example:  the so called dry powder extinguishers spread a powder layer on the materials, preventing oxygen to feed the fire.On the other hand, common carbon dioxide extinguishers produce a gas fog, for the same purpose:  keep the oxygen away!

When possible, we take out the other reactant, fuel. In wildfires, this can be done with an anti-fire or opening a firebreak, which is basically a strip of land with no vegetation.

Some examples of the use of chemicals in fighting fires require more in-depth knowledge of chemistry. Such is the case of “Halon” extinguishers and their more ecofriendly substitutes, like heptafluoropropane. These are compounds with a very effective extinguishing effect, because they interfere directly in the combustion chemical reactions, inhibiting them.

The diversity of combustible materials that surround us has contributed to increase the complexity of firefighting. But, since fire is a chemical reaction, we can count on the developments of chemistry to better understand and control it!