When a candle is burning, the combustion process is taking place efficiently. The flame's heat vaporizes the liquid wax, which then mixes with the surrounding oxygen and burns, producing carbon dioxide (CO2) and water vapor (H2O) as byproducts. In an ideal burning process, there is complete combustion, resulting in a clean flame with minimal smoke.
However, when a candle gets extinguished, the combustion process is disrupted. The absence of a continuous flame means that the liquid wax is no longer being efficiently vaporized and burned. Instead, it undergoes incomplete combustion. Incomplete combustion occurs when there is limited oxygen supply, insufficient heat, or an improper fuel-to-air ratio.
During incomplete combustion, the unburned hydrocarbon molecules in the liquid wax break down incompletely, leading to the production of carbon particles (soot) and other volatile compounds. These carbon particles form visible smoke as they are released into the air. Additionally, the lack of a stable flame means that there is not enough heat to fully vaporize the wax, further contributing to the production of smoke.
The sudden increase in smoke production when a candle is extinguished is a result of this incomplete combustion process. It is worth noting that the smoke produced after extinguishing a candle can also be accompanied by a distinct odor, which is due to the presence of various volatile compounds released during the incomplete combustion.