Why is fire hot?

October 12, 2008 2:49 AM

Why is fire hot?
posted by Taksi Putra to grab bag (7 comments total)

Because it's exothermic.
posted by knave at 3:12 AM on October 12

It takes energy to hold together Carbon and Hydrogen and Oxygen into wood molecules. When the wood molecules are broken down into char molecules and smoke molecules (by using a match to light some wood—by adding more energy),

6C10H15O7 + Heat → C50H10O + 10CH2O

those char and smoke molecules take less energy to hold together. The leftover energy is released in the form of heat and light. The released heat energy is used to loop the process and warm your hands until the fuel (wood) is exhausted or you tire of laymen's explanations.
posted by carsonb at 3:14 AM on October 12 [11 favorites]

There is more energy in the molecular bonds in oxygen and your fuel than there are in the combustion products (usually carbon dioxide and water). That energy has to go somewhere. It ends up as light and heat.
posted by Kid Charlemagne at 6:22 AM on October 12

Molecular motion. Move the temperature slider and observe the speed of the molecules.
posted by weapons-grade pandemonium at 10:01 AM on October 12 [1 favorite]

..and the difference in the number of collisions per second.
posted by weapons-grade pandemonium at 10:04 AM on October 12

Are you asking why fire releases heat or why it feels hot?
posted by junesix at 10:27 AM on October 12

Fire is a chemical process that quickly releases energy from matter. Sudden release of energy is going to feel hot to you.

If this is really a serious question then I would think this wikipedia entry would explain it better than most people here:

http://en.wikipedia.org/wiki/Fire
posted by damn dirty ape at 10:58 AM on October 12