Why Does a Candle Keep Burning While Plain Wax Doesn't?

It is a common misconception that plain wax does not burn. In reality, the melted waxmigrates up the wick to serve as fuel for the candle flame. If you interrupt the completion of the combustion by placing a metal object such as a nail or a pin into the flame, you will notice soot forming where it should not typically appear.

Understanding the Chemistry of Candle Burns

The species that are combusted in a wax candle are primarily methane, ethylene, and propane, which are found in the wax. These volatile hydrocarbons are dissolved in a solution of longer-chain alkanes. Ethylene, in particular, combusts according to the following chemical equation:

[H_2CCH_2 (g) 3O_2 (g) rightarrow 2CO_2 (g) 2H_2O (l)]

Wax and Wick Dynamics in Candle Burning

Heated wax is fluid and soaks into the wick, ensuring a continuous supply of fuel for the flame. Even after the last solid wax has melted away, there may still be some wax left in the wick. When the concentration of wax within the wick becomes too low, the wick itself can begin to burn, causing the candle to lose height.

Role of the Wick in Flame Maintenance

The wick is crucial for maintaining the flame. It provides a path for the wax to rise and burn, ensuring a steady and controlled combustion. In addition, the presence of oxygen around the wick allows the fire to continue burning, contributing to the candle's longevity.

Other Factors Affecting Candle Burning

There are several factors that can influence the burning of a candle, including:

Wax Quality: Higher-quality wax, often referred to as fresh wax, is more likely to burn cleanly and efficiently. Recycled wax from spent candles may contain impurities that can affect the burning process.

Temperature and Humidity: Environmental conditions can also impact the rate and efficiency of candle burning. Higher temperatures and lower humidity levels can lead to more rapid evaporation of the wax and faster combustion.

Wick Size and Composition: The size and composition of the wick can significantly affect how well the candle burns. A well-sized wick ensures optimal fuel delivery and provides a more consistent flame.

Conclusion

In summary, a candle does continue to burn because of the continuous supply of melted wax moving up the wick as fuel, the presence of oxygen, and the wick's role in maintaining the flame. Understanding the chemistry and mechanics behind candle burning can help explain why a candle keeps burning long after plain wax would otherwise cease to do so.