Eli5: How does charcoal work?


So when you burn wood, you get charcoal. Charcoal is carbon, right? Well then why does it burn if you buy a bag of charcoal? And what’s that gray soot stuff that’s leftover after the charcoal is burned? Is that pure carbon? Could someone explain the stages of burning wood like I’m 5?

In: Chemistry

So yes charcoal is carbon, but so is coal. In those cases the carbon has formed a stable structure with other carbons, hydrogen and oxygen. The result is a black flakey solid. However in the right conditions that solid can be broken down again.

With enough heat and a lack of oxygen the black solid (referred to as “char”) can undergo a process called pyrolysis aka “gassification”. This is usually a self sustaining reaction.

When you start the charcoal with the lighter fluid you create that high heat and low oxygen as the lighter fluid burns. This starts the pyrolysis where the char will break it’s bonds with the hydrogen and oxygen producing carbon dioxide, carbon monoxide, and hydrogen gas and a new white colored solid

When chemical bonds break like that they release heat which breaks the other bonds, allowing the pyrolysis to sustain itself. That’s why in campfires you’ll find white and black ash as the internal wood underwent pyrolysis but the external wood had more access to oxygen.

When wood is heated, it releases gases. These gases are what produce the big flame as they burn, although if charcoal is made in a container then there must be a hole for them to escape through. Once these gases are exhausted, only two things remain: Carbon and ash. Ash is a variety of random stuff, such as potassium oxide, that doesn’t become a gas when it reacts with oxygen. This is charcoal.

When charcoal burns, you’re left with *just* the ash, which is more or less impossible to burn and actually works well in putting out fires.

In a wood fire, the charcoal/carbon and gases burn sort of simultaneously, although the gas tends to go first and leave the hot burning coals at the bottom. Just burning the wood normally doesn’t produce usable charcoal, and you have to heat it without burning it if you want significant amounts of usable charcoal.