- #1
RubinLicht
- 132
- 8
I never really had a good idea of the mechanisms behind color. why we feel heat, what determines the color of fire, etc. So, today I sat down and did some research. I want to explain the processes here to make sure I got it completely right:
For complete combustion of most hydrocarbons (blue flame, this would be for gaseous hydrocarbons):
the hydrocarbon breaks down into carbon monoxide, however carbon monoxide is only meta-stable, and quickly combusts and turns into CO2. CO2 is formed in an excited state, and releases blue light when its electrons return to a lower energy state.
For incomplete combustion of most hydrocarbons (gaseous hydrocarbons without enough oxygen, and wood):
the hydrocarbon breaks down into carbon monoxide as usual, but there is some residual carbon from this reaction, which appears in the form of soot. The soot is heated up to temperatures that make it emit red-orange-yellow light due to thermal radiation (rather than atomic transitions like before). This overpowers most of the atomic transitions that are still happening, though much more weakly than before.
For odd colored flames like magnesium, sodium, copper, etc.
the heat vaporizes the metal (not sure about this part), and the vaporized metal floats away in an excited state, and when the electrons drop down to a lower energy state, the atom emits a photon of some energy, which determines the color of these flames.
so really, the color of fire is determined by two very different processes, either atomic transitions or thermal radiation. which mechanism is dominant depends on what chemicals are used.
question: When green fire is produced by holding a sample of copper above a yellow flame, the fire is often entire green beyond the point where it contacts the copper. is this because there is more green light being emitted than yellow light? does the soot maybe cool down (and fall out of the red-orange glowing temperature range) after heating up the metal atoms? some other mechanism?Looking forward to any constructive criticism.
For complete combustion of most hydrocarbons (blue flame, this would be for gaseous hydrocarbons):
the hydrocarbon breaks down into carbon monoxide, however carbon monoxide is only meta-stable, and quickly combusts and turns into CO2. CO2 is formed in an excited state, and releases blue light when its electrons return to a lower energy state.
For incomplete combustion of most hydrocarbons (gaseous hydrocarbons without enough oxygen, and wood):
the hydrocarbon breaks down into carbon monoxide as usual, but there is some residual carbon from this reaction, which appears in the form of soot. The soot is heated up to temperatures that make it emit red-orange-yellow light due to thermal radiation (rather than atomic transitions like before). This overpowers most of the atomic transitions that are still happening, though much more weakly than before.
For odd colored flames like magnesium, sodium, copper, etc.
the heat vaporizes the metal (not sure about this part), and the vaporized metal floats away in an excited state, and when the electrons drop down to a lower energy state, the atom emits a photon of some energy, which determines the color of these flames.
so really, the color of fire is determined by two very different processes, either atomic transitions or thermal radiation. which mechanism is dominant depends on what chemicals are used.
question: When green fire is produced by holding a sample of copper above a yellow flame, the fire is often entire green beyond the point where it contacts the copper. is this because there is more green light being emitted than yellow light? does the soot maybe cool down (and fall out of the red-orange glowing temperature range) after heating up the metal atoms? some other mechanism?Looking forward to any constructive criticism.