Why do some things melt and others burn to a crisp



Pretty much the title. For example, When being burned wood burns to charcoal but things like metal melt and turn into a liquid?

In: Chemistry

It’s the difference between adding heat and reacting to oxygen, and just adding heat. If the thing you’re heating up changes to something else with oxygen+heat then it burns, turning into some other combination of things (ashes and carbon dioxide)

First of all it’s worth noting that the way things react to heat here on Earth is heavily controlled by the air around us. The air does a lot of things. First, it squeezes things together, which is called atmospheric pressure. In the vacuum of space, most things can’t become liquid because without the air squeezing it together the atoms don’t stay around each other in that “liquidy” sort of way. Another thing the air does is provide oxygen. Nothing burns without oxygen. If you heat a piece of wood in space, it will never burn no matter what you do.

If we’re talking about things on Earth though, the answer is basically that all solids have one temperature at which they’ll stop being solid, and if it can interact with oxygen it will have another temperature for that. The question then becomes which one is lower. Wood burns at a *much* lower temperature than it would take to make the entire log something other than a solid. On the other hand, metal, which is far more stable on its own and less likely to interact with oxygen, will turn into a liquid first (metal can still burn but it’s very slow and takes more oxygen than the air can usually give it).

Going to pile on here: couldn’t you just remove all the oxygen instead of using a vacuum and prevent burn before melt that way?

Also, I would guess wood would melt in a way similar to sugar (sucrose), since cellulose is just a sugar?

Substances that burn instead of melt have combustion temperatures that are lower than their melting points. Before they have a chance to be heated to a temperature high enough to melt, they react with oxygen in the atmosphere and combust or burn. This is the case with wood.