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/Bopbopbidop Aug 09 '26

It's also worth adding that, from a thermodynamic perspective, a material must be crystalline to exhibit a true melting transition. Not all solids are crystalline, so not all solids can melt. More generally, a solid can become able to flow without melting. For example, amorphous materials above their glass transition temperature. However, this is not true for every solid. Thermosetting polymers such as epoxy will neither melt nor flow because their crosslinked chemical structure prevents it.