how can fire be different temperature?
In: Chemistry
A fire is a chemical reaction. You can imagine a molecule to be atoms (little marbles) linked by springs. All of the springs have difference stiffness, so breaking a spring releases energy, and the exact amount depends on a lot of things. When you create a new spring elsewhere, you create it with some energy.Take methane, for example. It’s something that burns quite easily, it’s formula is C1H4 : you have one ‘marble’ of carbon, 4 ‘marbles’ of hydrogen and 4 springs, each one between the Carbon at the centre, to one Hydrogen around. When you burn it, you destroy the 4 springs, you take two O2 (that’s two marbles of oxygen, linked together by a spring), and destroy those two springs too. Now you take the carbon, two oxygen and create two springs between the C and the two Os (that’s CO2, carbon dioxide), and to do this you need some energy. Good news, you had some in your pocket since you broke all the springs at the beginning.
Now you have to end the reaction, and you will create two molecules of water H2O. Once again, you need to create ‘springs’ to do this, and this requires energy.
Overall, if you had more energy by breaking the old bounds (that’s the real name for the springs) that you need to create the new ones, you will have at the end some energy left, and it will be heat : temperature rises.
So, different fires will have different temperatures because temperature is related to heat, and the heat released depends on the chemical reaction (that is, on what “burns”).
Fire is a chemical reaction between an oxidizer and a fuel source. Different combinations all combust at different points, so the intensity of the thermal radiation produced by the chemical reaction will vary.
Water can be different temperatures, it can be hot or cold. (But it has to be between 32-212 °F.)
Ice can be be different temperatures, it can be cold, or really cold. (But it has to be colder than 32 °F.)
Fire can be different temperatures, it can be hot, or really hot. (There is a minimum temperature, but it varies on material)
The temperature of a fire depends on how much heat is being produced by the combustion and how quickly it dissipates. If you lit a candle, it will not produce a lot of energy, and this energy will dissipate quickly because the air all around the flame is cold, so the temperature will not be too high. In a big fire, a lot of energy is being produced, and the hot air in the center is surounded by more hot air, so the heat dissipates slowly. This causes the temperature to rise inside the fire. This is how a furnace works, you burn something that doesn’t necessarily produce a lot of energy (like wood) but this energy has nowhere to go, so the temperature raises a lot.
That’s why the “jet fuel can’t melt steel beams” meme is bullshit. The twin towers were essentially a huge furnace.
Different material contain different amounts of releasable energy. When they get lit on fire that energy is used up by the fire.
Fire (as in the flames you see) is a side product of the burning process (which is the chemical reaction). Different materials can burn at different rates giving off different amounts of heat. The visible flame is also dependent on the intensity of the burning and the material. Some burning processes don’t even emit visible light (to humans at least).
For example magnesium can burn at ~3,100 °C (5,610 °F) with a bright white flame, whereas wood will start burning as “low” as ~300 °C (572 °F) with reddish-orange flames, but can reach ~1,100 °C ( 2,012 °F) with bright yellow flames.
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