A burning candle involves a chemical reaction. This process transforms the candle wax and oxygen into new substances, releasing energy in the form of heat and light.
What Makes a Chemical Reaction?
A chemical reaction is a process where substances change into new substances with different compositions and properties. This transformation occurs when existing chemical bonds between atoms are broken and new bonds are formed. Reactants are the initial substances that interact, while products are the newly formed compounds. Chemical reactions often involve an energy change, either releasing it (exothermic) or absorbing it (endothermic).
A change in temperature or the production of a gas are also signs of a chemical reaction. For example, the rusting of metal involves iron reacting with oxygen to form iron oxide, a new substance with different properties than the original iron. Similarly, baking a cake combines ingredients that undergo chemical changes to create a new product.
The Science Behind a Burning Candle
When a candle is lit, the heat from the flame initiates a series of events. First, the solid wax near the wick melts into a liquid, which is a physical change. This liquid wax is then drawn upward through the wick, much like water in a straw, due to capillary action. The heat of the flame then vaporizes the liquid wax, turning it into a hot gas.
The gaseous wax, primarily composed of hydrocarbons (molecules containing hydrogen and carbon atoms), then mixes with oxygen from the surrounding air. This is where the primary chemical reaction, known as combustion, takes place.
This process is a self-sustaining chain of events. The flame’s heat ensures continuous melting and vaporization of the wax, providing a steady supply of fuel for the ongoing combustion.
The Outcomes of Candle Combustion
Main products of complete candle wax combustion are carbon dioxide (CO2) and water vapor (H2O). These new substances are formed as the carbon and hydrogen atoms from the wax combine with oxygen. The energy stored in the chemical bonds of the wax is released during this exothermic reaction.
This released energy manifests as the heat and light that are characteristic of a burning candle. While complete combustion primarily yields carbon dioxide and water, incomplete combustion can also occur, especially if there is insufficient oxygen. In such cases, additional products like soot (fine carbon particles) and carbon monoxide (CO), a colorless and odorless gas, can be produced. The visible yellow glow of a candle flame is often due to these hot soot particles.