Why does a candle keep burning after it is lit?
The short answer
A candle keeps burning because its wick carries melted wax near the flame. Heat turns the wax into vapor, which reacts with oxygen in the air. That reaction releases more heat, melting more wax.
The cycle is: wax melts, liquid wax moves up the wick, and wax vapor burns.
- Wax melts: Heat from the flame melts the solid wax around the wick.
- The wick carries it upward: Liquid wax moves through tiny spaces in the wick.
- Wax vapor burns: Near the flame, the wax becomes vapor and reacts with oxygen, releasing heat and light.
The wick carries liquid wax toward the flame
When a candle is first lit, a match or lighter provides the heat that melts the wax beside the wick. Many wicks are made of fine fibers. Liquid wax moves upward through the tiny gaps between them, so the wick acts like a path that brings fuel close to the flame.
The movement of a liquid through narrow spaces is called capillary action. The wick is not a pump pushing wax upward. Its small spaces help the liquid wax travel toward the hot end.
Wax vapor is the flame’s main fuel
As liquid wax reaches the hot area near the flame, it warms further and turns into vapor. The flame’s main fuel is this wax vapor, not the solid candle. The vapor reacts with oxygen from the surrounding air. This chemical reaction is called combustion, and it releases heat and light.
The wick can burn too, but it is not the candle’s only fuel. The wick carries wax to the flame, and the wax vapor provides most of the fuel that keeps an ordinary candle burning.
Heat and moving air keep the cycle going
Heat from the flame melts more solid wax beside the wick. That liquid wax travels upward, turns into vapor, and reacts with oxygen again. The heat from one round of burning helps prepare fuel for the next.
Air warmed by the flame rises, and surrounding air moves in to take its place. That brings fresh oxygen toward the flame. As long as wax vapor, oxygen, and enough heat are available together, combustion can continue.
Why does blowing on a candle put it out?
Blowing cools the gases around the flame and spreads the wax vapor out. The flame can no longer keep a hot enough area with enough wax vapor for combustion to continue. Your breath contains oxygen, so blowing does not put out a candle simply by removing oxygen.
A candle flame depends on more than its wick. The wick carries wax, heat turns some of that wax into vapor, and oxygen from the air lets the vapor burn.