Study Guide

Chemical Reactions - Combustion

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We Have a Burning Desire to Combust

Combustion reactions are an extremely important class of chemical reactions. These reactions are vital to our everyday lives. Do you drive around in a gas-fueled car? Or cook dinner on a gas stove? How do you keep yourself warm in the winter? The list of combustion reactions critical to everyday life goes on.

The combustion of fuels (wood, fossil fuels, peat) have heated and lit our homes and cooked our food for thousands of years. Our lives would be completely different if combustion reactions didn't exist.

Here's a diagram showing how combustion works.

A combustion reaction takes place when a fuel and oxygen react, producing heat or heat and light. Other recognizable combustion reactions include a burning candle or a nice toasty campfire. Who brought the s'mores? Anyone? 

Fire is an indicator of combustion. (Image from here.)

Combustion usually occurs when a hydrocarbon (meaning a compound composed of only carbon and hydrogen) reacts with oxygen to produce carbon dioxide and water. These reactions are highly exothermic which means they release energy, often in the form of heat. That's why combustion chemistry is used to heat homes and fuel cars.

hydrocarbon + oxygen → carbon dioxide + water

CH4 + 2 O2 → CO2 + 2 H2O

Combustion reactions can sometimes be tricky to balance so if you get stuck make sure you review the content in the stoichiometry guide about balancing equations.

One interesting thing to note is that combustion reactions cannot proceed once the oxygen is depleted. Have you ever put an upside down glass over a burning candle? Check it out. You'll notice that the candle will burn for a little while longer, but as soon as all of the oxygen in the glass is consumed, the fire will disappear. Pretty neat, huh?

Also, remember every combustion reaction needs a hydrocarbon as well. In the case of candles, the hydrocarbon is the wick.

Some more combustion action. (Image from here.)

Here is a nice video review if you're still feeling overwhelmed by combustion, or if you need extra help balancing combustion equations check out this video. 

Brain Snack

Ever hear of spontaneous combustion? Yep, there's a movie named after it.

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