- #1
acesuv
- 63
- 0
I thought red has a smaller wavelength than blue and therefore red has more energy than blue. So why is it that hotter flames glow with a blue color?
Why are higher energy flames blue?
- Thread starter acesuv
- Start date
-
- Tags
- Energy
In summary, while it is commonly believed that red has a smaller wavelength and therefore more energy than blue, this is not the case in flame colors. The blue color in hotter flames is due to CH radicals, while red flames typically indicate an inefficient combustion process with the formation of soot. The color of the flame is not directly linked to its temperature, as red flames can have a higher temperature than blue flames.
- #2
A.T.
Science Advisor
- 12,554
- 3,687
acesuv said:
- #3
acesuv
- 63
- 0
HmmmmmA.T. said:
- #4
SteamKing
Staff Emeritus
Science Advisor
Homework Helper
- 12,811
- 1,673
acesuv said:
Apparently, you were misinformed.
- #5
bigfooted
Gold Member
- 683
- 214
There is no direct correlation between the wavelength and the flame temperature.
The blue light comes mostly from CH radicals that are formed in the flame and emit light at around 430 nm. This can be clearly seen in e.g. natural gas cooking devices. This color is independent of the flame temperature, so if you would burn with a larger excess of oxygen, the flame temperature would drop, but the flame would still emit blue light (although it will be with less intensity). When a flame colors red then it is usually because the combustion is somehow not optimal (usually there is locally a lack of oxygen) and soot is formed in the flame. Soot is basically carbon molecules, and they glow orange/red in the flame. This happens for instance in candle flames. The extra radiation of the soot lowers the temperature of the flame, so there is some correlation between color and temperature but you can have 'red' flames with a higher temperature than 'blue' flames.
The blue light comes mostly from CH radicals that are formed in the flame and emit light at around 430 nm. This can be clearly seen in e.g. natural gas cooking devices. This color is independent of the flame temperature, so if you would burn with a larger excess of oxygen, the flame temperature would drop, but the flame would still emit blue light (although it will be with less intensity). When a flame colors red then it is usually because the combustion is somehow not optimal (usually there is locally a lack of oxygen) and soot is formed in the flame. Soot is basically carbon molecules, and they glow orange/red in the flame. This happens for instance in candle flames. The extra radiation of the soot lowers the temperature of the flame, so there is some correlation between color and temperature but you can have 'red' flames with a higher temperature than 'blue' flames.
FAQ: Why are higher energy flames blue?
Why do higher energy flames appear blue?
Higher energy flames appear blue because they emit shorter wavelengths of light, which our eyes perceive as the color blue. As the temperature of a flame increases, the amount of energy emitted also increases, resulting in a shift towards the blue end of the visible light spectrum.
What causes the difference in color between low and high energy flames?
The color of a flame depends on the temperature of the flame and the elements present in the fuel. Low energy flames, such as a candle flame, are typically yellow or orange because they are not hot enough to excite the atoms in the fuel to emit blue light. Higher energy flames, like a Bunsen burner flame, reach higher temperatures and are able to emit more blue light, resulting in a blue color.
Can other factors besides temperature affect the color of a flame?
Yes, besides temperature, the color of a flame can also be affected by the composition of the fuel and the availability of oxygen. For example, a green flame may indicate the presence of copper in the fuel, while a purple flame may indicate the presence of potassium.
Are blue flames always hotter than other colored flames?
Not necessarily. While blue flames are typically associated with higher temperatures, this is not always the case. The color of a flame can also be affected by the surrounding environment and the amount of oxygen available. For example, a blue propane flame may not be as hot as a yellow propane flame if the blue flame is starved of oxygen.
Is the color of a flame a reliable indicator of its temperature?
No, the color of a flame is not always a reliable indicator of its temperature. The color can be affected by various factors, and different fuels can produce different colored flames at the same temperature. To accurately determine the temperature of a flame, other methods such as spectroscopy or thermometry must be used.