A chemical process is something that starts with one or more
substances and produces new ones. Is combustion a chemical process?
What substances are produced?
What substances react? (Think of the fire triangle.)
When something either produces or uses energy, it's a good sign that a
chemical reaction is taking place. In combustion, is energy mostly
used or produced? Is this exothermic or endothermic? Name two forms
of energy that we're talking about.
Can you think of an experiment that shows that combustion uses
only a part of air? That is, after something burns in air, can you
prove that there is still some gas left over?
Name 5 places where combustion occurs in a controlled fashion.
Name 2 places where combustion occurs in an uncontrolled and
dangerous fashion.
Can a fuel be a solid? Name one.
Can a fuel be a liquid? Name one.
Can a fuel be a gas? Name one.
Can oxygen support combustion if it's not in a pure, gaseous state?
Can you give an example?
You open the oven to check your cookies, and you notice they're on
fire or smoking. What should you do?
If a candle falls on a pile of newspaper and a fire starts, what
should you do?
If somebody's clothes catch fire, they might panic and run
around. Why is this a bad idea? Usually, the best thing to do is make
them drop and roll, and if there's a rug or blanket handy to roll
in, that's even better. Why does this put out a fire?
Possible Answers:
Combustion is a chemical process whose reactants are a fuel and
oxygen. If the fuel is a hydrocarbon (wood, gasoline, wax, sugar,
etc.) the substances produced by complete combustion are water and
carbon dioxide. Other products, such as carbon deposits, creosote,
and carbon monoxide, are produced by incomplete combustion of
hydrocarbons.
Combustion is a process that produces more energy than it
consumes; therefore it is exothermic by definition. Heat and light
are two forms of energy produced.
Numerous possibilities -- I always encourage students to try experiments
they design. BEWARE! It can be very dangerous to heat an enclosed
gas or any sealed container. If it's possible to use an elastic
membrane (e.g., a balloon or rubber glove) to seal a container, the
proposed experiments may be able to be carried out. Safety first!
Teachers should try procedures first to ascertain hazards.
Controlled Combustion: car engine, candle, wood stove, gas stove,
Coleman lantern, cigarette lighter, bunsen burner, blow
torch, ... Uncontrolled Combustion: House fire, forest fire, flame
thrower, grease fire on a stove, fire cracker....
Yes! Liquid O² is used for launching the space shuttle and other
rockets. A solid form of O² was used in the sugar flare in my show.
Oxygen-rich solid compounds are used in fireworks. Careful storage
of such compounds is crucial in a safe laboratory--simply mixing them -->
--with certain fuels results in a dangerous volatile mixture.
Close the oven, turn it off, call an adult. Leave it shut until
you're sure that it has cooled off.
Blow out the candle (the source), pull unburning magazines or
other papers and fuel away and smother the flames with a towel
(preferably wet) or pour water or soda pop on it. Call a grownup.
Running fans the flames by continually providing air with a full
amount of O². Drop and roll reduces the amount of burning surface
exposed to air. Wrapping someone tightly in a blanket completely
removes O² from the fire, thus extinguishing it.
