Chemistry

How a Candle Burns



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A candle is a very simple and basic item, consisting of a wick being encased within a body of solid wax.

The wick is usually made of braided cotton, and contains a core made of a harder material so that the wick remains stiff. Traditionally, the core was made of lead, but that material was subsequently ruled out due to concerns over lead poisoning. Zinc has since become the safer substitute. Other materials used for making the core include paper and synthetic fibres.

For the wax portion, household candles are mostly made from paraffin. Paraffin is artifically manufactured, and is a low-cost petroleum-based wax. Other forms of wax, made of natural ingredients, include beeswax, soy wax and bayberry wax. These are much more costly compared to paraffin. There is also gel wax, which is clear and see-through.

Mechanics of a Burning Candle:
* The wick at the tip of a candle is usually coated on the outside with wax, or filled with wax inside. This bit of wax provides the initial fuel source when the wick is lit by a flame, the external catalyst.
* After being lit, the wick itself starts to burn first. Next, the flame slowly gets into contact with the wax of the candle at the base of the wick. From the solid state, the wax melts and changes to the liquid state.
* As the flame continues to burn, capillary action draws the liquid wax up to the tip of the wick. Capillary action works based on the tension created between the two walls of a thin tube. It is the way the roots of a plant bring in water from the surrounding soil to keep the plant alive. Through that same action, the liquid wax gets drawn up all the way into the flame.
* The liquid wax drawn to the tip of the wick becomes additional fuel for the flame to burn. In the process, the liquid wax gets heated up even more. It then vaporizes and converts from the liquid to the gaseous state.
* When the wax in its gaseous state enters the combustion zone of the flame, it gets converted into energy. This in turns emits heat. The heat generated then continues to melt more of the solid wax of the candle.
* At times, when the amount of liquid wax produced is greater than the amount that is being drawn up to the wick by capillary action, the liquid wax overflows the sides and form 'tears'. Being away from the source of heat, these 'tears' at the sides slowly cool down and solidify again.

The burning cycle described above is repeated for as long as the candle flame is burning. Over time, more and more of the candle wax becomes melted, converting from the solid to the liquid state, and then, the gaseous state. Consequently, the wick is burnt down and the candle diminishes in size.

If left alone and undisturbed, the candle will continue burning until all the wax (i.e. the fuel) is used up, and the wick is no longer functionable.

Other Factors that Affect the Speed of Burning:
* Thickness of the wick - A wick of a larger diameter results in a larger flame, which in turn creates a larger pool of melted wax. As a result, the candle will burn faster.
* Flatness of the wick - Wicks that are braided flat will curl back into the flame as they burn. This makes the wicks self-consuming and burn faster.
* Amount of oxygen - Oxygen is needed for combustion, so the more oxygen-rich the place, the better and faster the candle will burn.

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