Imagine sitting in entrance of a campfire. A smoky scent wafts by way of the air as a pot of soup simmers over the open flame. While you stare on the flickering orange tongues, you would possibly marvel: Why are the wooden logs on hearth, however the steel pot is not?
The motive why some issues catch hearth and different issues do not comes right down to their chemical bonds and the power it might take to vary or break these bonds.
But first, here is a primer on hearth itself. Fire wants a number of issues to exist: oxygen, warmth and gas.
Oxygen is a fuel that is within the air. Heat may be created with friction, like once you strike a match, or it may be created in different methods, equivalent to a lightning strike. Fuel is the factor that burns: Generally, this may be something made up of natural materials, Carl Brozek, a chemist on the University of Oregon, advised Live Science. In this case, “organic” refers to molecules which might be fabricated from primarily carbon-hydrogen bonds and typically embrace oxygen or different atoms, equivalent to phosphorus or nitrogen.
Related: What makes one thing fireproof?
Specifically, burning is a chemical response that releases power from an unstable system with comparatively weak chemical bonds. Everything needs to be extra secure, particularly natural molecules that comprise carbon, oxygen, hydrogen and some different parts, Brozek stated. Materials like wooden and paper, which catch hearth simply, are fabricated from cellulose — a molecule composed of bonds between carbon, hydrogen and oxygen.
And when one thing burns, it finally ends up “releasing a lot of energy because now you’re moving the system to a lower energy state,” Brozek stated. “And that energy has to go somewhere.”
When an object fabricated from wooden catches hearth, the cellulose that makes up the wooden is transformed to carbon dioxide and water vapor — each very secure molecules with sturdy bonds. The power launched by this chemical response excites the electrons within the atoms of fuel, which in flip emit seen mild. That mild seems to us as a flame, Brozek stated.
Back to the burning log versus the new pot of soup: The distinction between a log and a steel pot has to do with how nicely the fabric can distribute the power concerned when hearth is utilized to it, Brozek stated, which comes right down to how sturdy its chemical bonds are. The sturdy chemical bonds in steel cannot be damaged simply. A chunk of wooden, in the meantime, lacks these sturdy bonds, so it would not have the capability to soak up the power from the flame. Instead of absorbing the power, the wooden releases the power by catching hearth. But the steel within the pot “has a huge capacity to absorb that energy and dissipate it,” which is why the pot will really feel sizzling to the contact.
Better absorption of warmth may cease wooden from catching hearth. If a flame have been utilized to a paper cup stuffed with water, the cup would not burn, Brozek stated. Because the water within the cup can soak up the warmth, the paper will not catch hearth. (Although we do not suggest you do that your self.)
Some metals, nevertheless, do burn. Such “combustible metals,” together with potassium and titanium, are used to make fireworks. The metals in fireworks are in powder kind, which gives extra floor space for it to react a lot sooner with warmth and oxygen, Brozek stated. When these metals are uncovered to ample warmth to react with oxygen, the quantity of power launched causes them to burn in several colours.
Originally printed on Live Science.