A chemical reaction can produce heat. Combustion is a type of heat-producing chemical reaction. The wax of a candle is a fuel that contains large amounts of carbon. When the candle burns, or combusts, its carbon reacts with the oxygen in the air around it. As a result, the oxygen and carbon dioxide are joined together into carbon dioxide (pictured on the right). 

The material that constituted the candle does not disappear during combustion. Instead, it takes a new form. Substances never disappear, but they can take new forms. This is how the elements continue their endless cycle on planet Earth. 

Candle wax also contains hydrogen, like all other fuels. When hydrogen combusts, it forms water or dihydromonoxide (pictured below).

When hydrogen reacts with oxygen, the result is water.

Although the air around it contains large amounts of oxygen, the candle cannot burn by itself. In addition to a fuel and oxygen, combustion also requires energy. This energy can be supplied with a match. The heat produced by friction is enough to light the tip of the match on fire. The match can then be used to light the cotton thread of the candle. 

The lowermost part of the candle's flame looks empty. However, this is not the case. It is actually made out of transparent wax gas. The heat of the candle first transforms the wax into molten liquid and then transforms it into gas. The burning wax gas produces the candle's flame. 


Combustion also requires energy. Usually, this energy comes in the form of heat. The friction that is produced when striking a match creates enough heat for the tip of the match to light on fire. The match can then be used to light the candle.

Above the empty area of wax gas at the bottom of the candle, you can find a blue flame. It is where actual combustion takes place. Here, the air's oxygen molecules is combined with the wax molecules. This produces a high heat. The blue flame of the candle does not produce a lot of light. 

The most visible part of the candle's flame can be seen in white. It is the light-producing part of the flame. When the candle's wax gas burns, some of its carbon can escape in the form of soot. The hot soot begins to radiate light. The phenomenon is similar to those found in incandescent light bulbs, where a hot metal string is used to produce light. 


The blue area of the flame is where the actual combustion reaction takes place. The white area of the flame consists of hot soot that radiates light.