When a candle burns, it undergoes a fascinating transformation that involves both physical changes and chemical reactions. What appears to be the simple disappearance of solid wax is actually a complex process converting it into new forms of matter and energy. Understanding this process reveals where the candle’s substance truly goes.
From Solid to Gas: The Physical Journey of Wax
The visible wax of a candle does not burn directly in its solid form. Instead, the heat from the flame initiates a physical change, causing the solid wax around the wick to melt. Different types of wax have varying melting points. This creates a small pool of liquid wax at the base of the wick.
The liquid wax is then drawn upward through the wick by a process called capillary action. This is similar to how a sponge absorbs water. As the liquid wax reaches the hotter tip of the wick, the intense heat from the flame causes it to vaporize, turning into a hot gas. This gaseous form of wax, composed primarily of hydrocarbon molecules, is the fuel that interacts with the flame.
The Chemical Transformation: What Wax Becomes
Once the wax has vaporized, it undergoes a chemical transformation known as combustion. The gaseous wax molecules mix with oxygen from the surrounding air and ignite, producing the visible flame. This reaction releases both heat and light, sustaining the continuous melting and vaporization of more wax, keeping the candle burning.
During complete combustion, the wax reacts fully with oxygen to produce two invisible gases: carbon dioxide and water vapor. These products disperse into the air, making it seem as though the wax has simply vanished. However, conditions are not always perfect, leading to incomplete combustion. When there is insufficient oxygen or the flame is disturbed, not all of the wax vapor burns completely.
Incomplete combustion can result in the formation of other substances, notably soot and carbon monoxide. Soot consists of tiny, unburned carbon particles that become visible as black smoke or residue. Carbon monoxide, a colorless, odorless, and tasteless gas, can also be produced during this process. While a well-burning candle produces minimal amounts of these byproducts, their presence explains what happens to the wax that doesn’t fully convert into carbon dioxide and water vapor.