# Why are fires smokey?

Combustion, in chemical terms, is a reaction with a certain molecule and oxygen, and it produces, energy, $\ce{CO2}$, and $\ce{H2O}$ (That's how I learned it at least). So what makes a fire'smokey'? I had always thought that smoke was simply $\ce{CO2}$, but read that it was actually the result of incompletely 'combusted' material, yet I don't fully understand what this means. Is smoke made from material that starts to combust but stops before it finishes, or does it never even begin combustion? What would the chemical reaction be of a wood (Or other similar) fire that produces a lot of smoke? And finally, is there a certain element or compound that gives smoke its 'smokey' smell?

• – Mithoron Feb 14 '16 at 16:58

Fires need oxygen to burn properly. By that I mean if there isn't sufficient oxygen supplied to the fire, the material that is burning does not completely burn up. They come to the middle of the combustion reaction but they run out of oxygen. These bits of incomplete combustion are called soot or smoke. $\ce{CO2}$ is another by-product of combustion. There are particular woods that give off certain smells and flavours like hickory, but smokey smells are probably only caused by carbon.