At first glance, a burning candle might look like a simple household object. When looked at closely there are several phenomenon that take place such as; capillary action, collision theory, and incandescence.

  When a candle is first lit, the wick might burn for a short time, but the wick is obviously too small to allow the candle to burn for extended periods of time, like most candles do. During the lab, our group tried burning some string that could be used for a wick, but without the wax. The string burned very quickly, and then went out in under 30 seconds. This means that the wax in the candle must be traveling up the wick to be burned. We also tried burning liquid and solid wax, and it would not burn. What happens, is when you light the wick, some of the wax is turned into a vapor form which can then light on fire. When the gaseous wax ignites, some of the wax at the base of the wick will be turned into a liquid. The liquid wax is brought up the wick by capillary action, and by the heat of the flame already burning, the wax is vaporized, and burned. This will continue until there is no more fuel to burn.

During the lab, we tried to use the end of a match as a wick, but when we lit the match, it burned down to the wax, but did not continue to burn. This happened because the paper the match was made of was not absorbent enough, and capillary action could not take place quickly enough to support a flame for very long.

The flame on a candle is very controlled, because the surrounding pool of wax cannot be burned without being vaporized first by the wick. When we inverted a beaker, and put the opening of the beaker over the flame of the candle, water started condensing on the outside of the beaker. This happened because every chemical equation has to be balanced. The equation for the paraffin wax burning looks like this; C25H52+38O2 H2O+25CO2. This means that the 25 carbon molecules and the 52 hydrogen molecules combine with 76 oxygen molecules to form water and carbon dioxide.

When we put the bottom of the beaker into the flame, carbon black built up on the bottom of the beaker. This is because of collision theory. Collision theory says that particles must collide with sufficient velocity to break bonds, so new bonds can form. When the carbon molecule are released from the burned wax, they collide with the bottom of the beaker before they can collide with oxygen molecules to form carbon dioxide, and water.

We blew out the flame and then quickly lit the smoke coming up from the wick with a match. The smoke lit on fire, and traveled down and lit the wick. Our group concluded that this happened because there was still some wax vapor in the smoke that lit, and the wick still had enough liquid wax left on it to quickly vaporize some of it and relight the candle once again.

During the lab we also put a piece of copper wire into the flame to see what would happen. The base of the flame in a candle is 800°C the top of the flame is 1400°C because all of the wax has had a chance to burn. In the fire the copper wire turned red, orange, and then yellow before the wire melted. This is called incandescence. The copper wire follows the visible light spectrum as it gets hotter, until it reaches its melting point.

Although a candle might look very simple several things happen such as capillary action, collision theory, and incandescence that you really have to take a closer look to fully realize what is happening.

Image via Wikipedia