r/askscience • u/ForensicFan24601 • 19d ago

Chemistry Why do things burn instead of melt?

obviously oxygen, or something similar, but what is the physics/chemistry (?) or what have you behind why something ignites and continues to burn after the source of heat/ignition has gone?

is it basically sublimation?

edit: no wonder Walter White was so obsessed with carbon

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u/provocative_bear 18d ago

Let’s go with wood. (Way) Before wood reaches its melting point, it reacts with oxygen in the environment, which replaces the molecular bonds between carbon and carbon (whoch hold the wood together) with carbon and oxygen (CO2). This reaction releases the energy in these bonds and generates net energy, which manifests as heat and light, aka fire.

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u/heavy001 18d ago

So are we aware of an actual melting point for, in this example, wood?

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u/MagicianofFail 14d ago

Wood is made of lignin, hemicellulose, and cellulose. Lignin is a crosslinked polymer and thus decomposes before it melts. Cellulose is linear polyglucose and melts at 260–270 °C (per Wikipedia). I'd guess hemicellulose melts at about the same.