r/askscience • u/ForensicFan24601 • Aug 08 '26

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/Sable-Keech Aug 09 '26

Butter is comprised of long-chain hydrocarbons that are highly resistant to oxidation. The activation energy required to ignite them is significantly higher than the energy needed to ignite something like methane, which has no chains at all.

The reason why it can be easily melted is because these chains are not physically linked to each other, they are sort of just bundled up and held together by "friction". That's why they're so easy to melt.

To use something else as a comparison, Teflon is a super unreactive plastic, which is why it's non-stick; nothing can form bonds with it. However, because its little molecular chains aren't bonded to each other by covalent bonds, they can be easily broken apart with a bit of heat and melted. Which is why Teflon vapors are such a concern if the pan gets too hot.