Fire: Why Blue is hotter than Red and What it Is.

When it comes to understanding fire, the first point I must make is that fire is a chemical reaction.  The physics/chemistry involved in fire is just fascinating. 


Here's what I'm going to cover:

• How Fire is a chemical reaction.
• Why Fire produces light and heat.
• What the different colors in fire mean.

To truly understand how it works we need to understand a few things about atoms.  Atoms are of course made of particles called electrons, protons and neutrons.  Which one plays an important part in chemical reactions?  Electrons have the most influence there.  Protons can play a large part in chemical bonding.



So what's the deal with electrons?  As you know they have a negative charge and they orbit the nucleus of the atom.   What you may not have known is that electrons orbit at specific energy levels.  If an electron moves to a different energy level it must either gain or lose the exact difference in energy levels.

A simple atom in ground state.  The blue is the electron (-) and the purple/pink is the proton (+).

What happens when the energy is gained?  Well the energy must come from somewhere.  "Energy cannot be created nor destroyed" it can only change form. This is why fires can start when it's hot.  If you heat something that is combustible you a giving the electrons energy in the form of heat.  Heat is a form of light, contained in the infra-red spectrum.  Our body interprets infra-red as heat.

This shows hoe our simple atom is excited, and the difference in the energy levels.

All forms of matter prefer being in an non-excited state (the ground state), the state that requires the lowest form of energy it can.  So after an electron is excited it wants to return to the ground state.  Thus the electron gives away the energy it absorbed by releasing it in the form of light.  The light can be all along the spectrum of light.  What states the electron changes between determines the wavelengths of light produced.

This shows how the electron returns to the ground state.

Here we have the spectrum of light, from Radio to Gamma waves, in increasing energy.  Showing how the visible red light is less energetic than visible blue or purple light.

The color of the visible light results from the energy. Blue light is more energetic than red light, which is why a blue fire is hotter than a red fire, it has more energy it is giving off.

This also is true in Astronomy, a blue star is much hotter than a red star. But “what burns twice as bright burns half as long” and maybe the numbers are not exactly true, the idea is, a blue star burns out much faster than a red star.  The hotter a reaction is the more fuel is used up at once. When the fuel is gone the reaction is over.

At night a blue light is much more blinding than a red light because our eyes have adjusted to the dark by dilating or expanding to let more light in.  When we are exposed to that energetic light we receive a lot more energy than our eyes were expecting.  This causes our pupils to shrink very quickly, the combination of all the light and the rapid shrinking causes pain and overwhelms our eyes which is why it is difficult to see afterwards.  When exposed to red light our eyes don't need to shrink much, if at all, so we can stay dark adapted.

To summarize...
Fire:

• A chemical reaction resulting in heat and visible light
• Purple/Blue Fire > Yellow/Red Fire (in energy)

Additional Information
 NASA explains Fire

Need more clarification?  This Richard Feynman video should help!

Let me know if anything was confusing, and always keep asking questions!