Why can't candles burn in carbon dioxide?

Answer 1

For combustion to occur (that is, a fire to start), oxygen must be present. In an anaerobic environment where oxygen is not present, there can be no combustion reaction. Even though Carbon dioxide contains oxygen (the oxide in dioxide) it must exist as oxygen gas for a fire to start, the carbon and oxygen in CO2 are bonded so tightly that normal reactions cannot separate the two in order for the combustible material to use it. I'm having a hard time attempting to paint a picture of how this works. Imagine this, when a person or animal suffocates due to "lack of oxygen" it is not actually the lack of oxygen that kills them, it is the over abundance of carbon dioxide. When you breath in, you are breathing in everything in the atmosphere, oxygen, carbon dioxide, nitrogen and argon. Your body utilizes the oxygen, nitrogen and argon, but it cannot utilize the CO2 so you get rid of it when you exhale. When put into an airtight environment eventually you will have replaced most of the oxygen with carbon dioxide and will only be breathing the CO2 in and since the bonds are too strong for your body to break the carbon and oxygen apart the carbon dioxide is useless to us and our organs and blood do not get the oxygen they need and suffocation occurs. Hopefully this will help you understand a little better that nothing can remove the oxygen from carbon dioxide and like our bodies a flame cannot sustain life with carbon dioxide alone.

Answer 2

The candle wax is mostly a hydrocarbon which, when exposed to oxygen in the atmosphere and ignited, oxidizes. The hydrogen combines with oxygen to form water and the carbon combines with oxygen to form carbon dioxide. However if you deplete the oxygen (don't provide adequate ventilation), carbon monoxide (CO) will also be be produced.