Think about sitting in entrance of a campfire. A smoky scent wafts by the air as a pot of soup simmers over the open flame. When you stare on the flickering orange tongues, you would possibly marvel: Why are the wooden logs on hearth, however the metallic pot is not?
The rationale why some issues catch hearth and different issues do not comes all the way down to their chemical bonds and the power it might take to alter or break these bonds.
However first, this is a primer on hearth itself. Fireplace wants a couple of issues to exist: oxygen, warmth and gas.
Oxygen is a gasoline that is within the air. Warmth will be created with friction, like while you strike a match, or it may be created in different methods, similar to a lightning strike. Gasoline is the factor that burns: Usually, this may be something made up of natural materials, Carl Brozek, a chemist on the College of Oregon, instructed Stay Science. On this case, “natural” refers to molecules which are made from primarily carbon-hydrogen bonds and typically embody oxygen or different atoms, similar to phosphorus or nitrogen.
Associated: What makes one thing fireproof?
Particularly, burning is a chemical response that releases power from an unstable system with comparatively weak chemical bonds. Every little thing needs to be extra steady, particularly natural molecules that include carbon, oxygen, hydrogen and some different components, Brozek mentioned. Supplies like wooden and paper, which catch hearth simply, are made from cellulose — a molecule composed of bonds between carbon, hydrogen and oxygen.
And when one thing burns, it finally ends up “releasing plenty of power as a result of now you are transferring the system to a decrease power state,” Brozek mentioned. “And that power has to go someplace.”
When an object made from wooden catches hearth, the cellulose that makes up the wooden is transformed to carbon dioxide and water vapor — each very steady molecules with sturdy bonds. The power launched by this chemical response excites the electrons within the atoms of gasoline, which in flip emit seen gentle. That gentle seems to us as a flame, Brozek mentioned.
Again to the burning log versus the recent pot of soup: The distinction between a log and a metallic pot has to do with how properly the fabric can distribute the power concerned when hearth is utilized to it, Brozek mentioned, which comes all the way down to how sturdy its chemical bonds are. The sturdy chemical bonds in metallic cannot be damaged simply. A bit of wooden, in the meantime, lacks these sturdy bonds, so it would not have the capability to soak up the power from the flame. As an alternative of absorbing the power, the wooden releases the power by catching hearth. However the metallic within the pot “has an enormous capability to soak up that power and dissipate it,” which is why the pot will really feel scorching to the contact.
Higher absorption of warmth may also cease wooden from catching hearth. If a flame had been utilized to a paper cup crammed with water, the cup would not burn, Brozek mentioned. As a result of the water within the cup can take in the warmth, the paper will not catch hearth. (Though we do not suggest you do that your self.)
Some metals, nonetheless, do burn. Such “flamable metals,” together with potassium and titanium, are used to make fireworks. The metals in fireworks are in powder kind, which supplies extra floor space for it to react a lot quicker with warmth and oxygen, Brozek mentioned. When these metals are uncovered to ample warmth to react with oxygen, the quantity of power launched causes them to burn in several colours.
Initially printed on Stay Science.