The short answer to whether candle wax evaporates is no. The apparent vanishing act of the wax when a candle is lit is a common misconception. Many assume the wax transitions directly into a gas that floats away, similar to how water disappears from a puddle. In reality, the disappearance of the candle’s material results from a complex process combining physics and chemistry. The wax is not evaporating; it is being consumed as fuel in a chemical reaction called combustion.
Evaporation Versus Combustion
Understanding the fate of the wax requires distinguishing between a physical change and a chemical one. Evaporation is a physical process where a substance transitions from a liquid to a gas, usually at a temperature below its boiling point, without changing its chemical structure. For example, evaporated water remains H₂O. Combustion is a rapid chemical reaction that occurs when a fuel source reacts with an oxidant, typically oxygen in the air, to produce heat and light. This reaction fundamentally changes the fuel’s chemical makeup. Candle wax, composed of long-chain hydrocarbon molecules, is broken down during combustion primarily into carbon dioxide and water vapor.
The Role of the Wick and Capillary Action
Before the wax is consumed, it must be delivered to the flame, starting with a phase change from solid to liquid. The heat from the flame melts the solid wax surrounding the wick, creating a pool of molten fuel. Waxes, whether paraffin, soy, or beeswax, are long-chain hydrocarbons that must be liquified to serve as fuel. Once liquid, the wick transports the molten fuel upward against gravity using capillary action. The wick is made of braided fibers, and the microscopic spaces between them create narrow channels that pull the liquid wax up toward the heat source.
The True Mechanism of Wax Consumption
The liquid wax drawn up the wick does not burn in its liquid state; it must first transition into a gas. When the molten wax reaches the hottest point of the flame, intense heat causes it to rapidly vaporize. This process transforms the liquid into a cloud of wax molecules, often called paraffin vapor, which is the immediate precursor to the flame. This gaseous wax vapor then mixes with oxygen in the air and ignites through combustion. The primary end products are carbon dioxide and water vapor, which disperse into the air, explaining the near-total disappearance of the wax mass.
What Happens to Remaining Wax
While the bulk of the wax is chemically consumed through combustion, small amounts are lost through other means. A negligible amount of true evaporation, or sublimation, can occur from the solid wax surface over long periods, even when the candle is unlit. This slow physical process involves solid wax molecules transitioning directly into a gas without melting, sometimes contributing to fragrance loss. Another minor loss occurs when combustion is incomplete, resulting in soot, which is composed of tiny particles of unburned carbon that escape the flame. Finally, when a candle is extinguished, the white plume of “smoke” rising from the wick is unburned wax vapor that has quickly cooled and condensed back into visible, microscopic solid particles.