The color of a flame is influenced by the materials being burned and the temperature of the combustion process. In the case of candles, fire, and gas stoves, the color differences in their flames can be explained as follows:
Candles: Candles typically produce a yellow flame. The color is mainly due to the presence of small soot particles in the flame, which emit yellow light when heated. The primary components of a candle flame are carbon (in the form of soot) and carbon dioxide. The flame's temperature is relatively lower compared to some other sources, which results in incomplete combustion, leading to the creation of soot and the yellow color.
Fire (Wood, Paper, etc.): Flames from burning wood, paper, or similar materials also tend to have a yellowish color. This is because the materials contain carbon and other impurities, which produce the yellow light as they burn. Again, the temperature of the flame plays a role in the color appearance.
Gas Stoves: Gas stoves usually have a blue flame. The blue color is an indicator of more complete combustion. When natural gas (methane) or propane is burned, the high temperature and efficient combustion process result in a blue flame. In this case, the blue color is not due to soot but rather due to the specific molecular composition of the fuel, which emits blue light when burned efficiently.
To summarize, the different colors in flames are primarily due to the chemical composition of the materials being burned and the efficiency of the combustion process. Yellow flames are often associated with incomplete combustion and the presence of soot, while blue flames indicate more efficient and complete combustion of clean-burning gases.