After a dinner party, the host performed the following trick. First, he blew out one of the burning candles. He then quickly brought a lighted match to about 1 in above the wick. To everyone's surprise, the candle was relighted. Explain how the host was able to accomplish the task without touching the wick.

Understanding the differences between physical and chemical changes is fundamental to grasping how a candle relights as demonstrated in the dinner party trick. A physical change involves a transformation in a substance's form or physical properties without altering its chemical composition. Examples include melting ice or breaking a piece of glass.

In contrast, a chemical change fundamentally alters the substance's chemical makeup, producing new substances altogether. This is precisely what happens during combustion—commonly known as burning. The candle wax, through the process of burning, chemically reacts with oxygen from the air to form water vapor and carbon dioxide. Even when the candle is blown out and smoke is observed, these are tiny wax particles that have undergone a physical change from solid to gas, but not a complete chemical reaction.

The act of relighting the candle with a match introduces enough heat to initiate a chemical change again, turning those wax vapors back into a combustion reaction that reignites the wick. Understanding the fine line between physical and chemical changes elucidates how the candle trick works without physically touching the wick.

The spectacle of relighting a candle flame without direct contact with the wick is essentially a combustion reaction, a chemical process typically involving oxygen and a fuel that produces energy in the form of light or heat. In the case of a candle, the fuel is the wax. This reaction is exothermic, releasing heat as the wax molecules react with oxygen in the air to form new products—water vapor and carbon dioxide.

When the candle is blown out, the wick smolders, producing smoke, which contains wax vapor that did not completely combust. By bringing a lit match close to the trail of wax vapor, you reintroduce sufficient heat to trigger the combustion reaction in the wax vapor. This is why the flame can travel 'magically' through the vapor back to the candle wick and reignite it. The concept of a combustion reaction is integral to understanding not only how candles burn but how we can manipulate these reactions for various effects, from relighting a candle to powering engines.

The interplay of the states of matter is showcased perfectly in the phenomenon of a candle burning and being relit. Initially, the solid wax near the wick is melted by the heat of the flame—an example of a phase change from solid to liquid. As the liquid wax is drawn up the wick by capillary action, it's then vaporized into a gas by the high temperature of the flame. This shifts the wax from a liquid to a gaseous state.

Once the candle is extinguished, the hot wax vapor begins to cool and condense into fine particles seen as smoke—another state change from gas back towards liquid/solid. However, when a burning match is introduced above the wick, it reheats the wax particles to a gas state before they fully condense, leading to the spectacular relighting of the candle flame. This dance between solid, liquid, and gas states is crucial for the burning process of a candle and is illustrative of how matter can change forms with the input or release of energy.