what happens when a candle is alight?
Paraffin vaporizes near the base of the wick and is convected upwards into the air. Particles of soot form that give off the light before they burn up at a reaction front. It is called a "diffusion flame" because the oxidizer and fuel come together from opposite directions.
This reference explains how a candle works better than I just did:
http://www.answers.com/topic/diffusion-flame?cat=technology
When a candle is alight, several chemical and physical processes take place. Here's an explanation of what happens:
1. Ignition: When a flame or spark is applied to the wick of the candle, the heat vaporizes the wax near the wick.
2. Wax Vaporization: As the wax near the wick vaporizes, it turns into a mixture of wax vapor and combustible gases, such as methane and ethane.
3. Combustion: When the wax vapor and gases mix with oxygen in the air, they undergo a chemical reaction known as combustion, producing heat, light, and new chemical compounds.
4. Flame Formation: The heat causes the vaporized wax and gases to rise upward in a process called convection, creating a flow of hot gases.
5. Blue Outer Flame: The outer, cooler zone of the flame appears blue and is where complete combustion occurs. This zone has excess oxygen, which results in the blue color.
6. Yellow Inner Flame: The inner, hotter zone of the flame appears yellow or orange. This zone has a lack of oxygen, causing incomplete combustion, and it contains partially burned carbon particles, which emit the yellowish glow.
7. Heat and Light: The heat produced by the flame warms the surrounding air, while the visible light is created as a result of incandescent carbon particles glowing.
8. Melting and Evaporation: The heat radiated by the flame melts and vaporizes nearby wax, continuously supplying fuel to sustain the burning process.
9. Wick: The wick, typically made of braided cotton, acts as a capillary, drawing liquid wax up to the flame, where it vaporizes and burns.
In summary, when a candle is alight, the heat from the flame vaporizes the wax near the wick, creating a mixture of combustible gases. These gases then undergo combustion, producing heat, light, and new chemical compounds. The visible flame is a product of the combustion process, while the heat and light are a result of the energy released.