When a candle burns, several chemical reactions take place, including combustion and pyrolysis. The primary products formed during the burning of a candle are carbon dioxide gas (CO2), water vapor (H2O), and soot (carbon particles). The overall chemical reaction for the burning of a candle can be represented as follows:

Combustion reaction:

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C25H52 + 38O2 → 25CO2 + 26H2O + energy (heat and light)

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In this reaction, the hydrocarbon molecules in the candle wax (C25H52) react with oxygen (O2) from the surrounding air to produce carbon dioxide (CO2) and water vapor (H2O). The energy released during this combustion reaction is emitted in the form of heat and light, causing the candle to burn and emit a flame.

Pyrolysis reaction:

In addition to combustion, pyrolysis (the thermal decomposition of organic matter in the absence of oxygen) also occurs during candle burning. This process leads to the formation of various intermediate products and by-products, including soot (carbon particles), hydrocarbons, and other organic compounds. These by-products are responsible for the characteristic scent and appearance of candle flames.

The relative proportions of CO2, H2O, and soot produced during candle burning can vary depending on factors such as the type of wax used, the presence of impurities, and the burning conditions. For example, candles made with certain waxes, such as soy wax or beeswax, tend to produce less soot compared to paraffin wax candles. Additionally, factors such as the size of the candle flame, the availability of oxygen, and the air currents in the surrounding environment can influence the burning process and the composition of the products formed.