As a domain expert in physical chemistry and thermodynamics, I can explain the process of why a candle runs out.

When you light a candle, you're initiating a chemical reaction known as combustion. The wax, typically made from hydrocarbons, reacts with oxygen in the air to produce water, carbon dioxide, and heat. This reaction is exothermic, meaning it releases heat, which is why the flame is warm to the touch.

The heat from the flame melts the wax near the wick, turning it into a liquid fuel. This liquid wax is drawn up the wick by capillary action. As the liquid wax reaches the top, it vaporizes and mixes with oxygen, which is necessary for combustion to occur. The heat from the flame then ignites this mixture, producing the visible light and heat we associate with a burning candle.

As the combustion continues, the wax is consumed, and the liquid wax that has been drawn up the wick is also used up. Over time, the wax supply depletes, and eventually, there's not enough left to sustain the chemical reaction. When the wick can no longer draw up enough wax to keep the flame going, the candle goes out.

In summary, a candle runs out because the wax, which serves as the fuel for the combustion reaction, is depleted over time through the process of melting, vaporizing, and burning.

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When you light a candle, you melt the wax in and near the wick. The wick absorbs the liquid wax and pulls it upward. The heat of the flame vaporizes the wax, and it is the wax vapor that burns. ... If you touch a lit match to the stream, a flame will run down it and re-light the wick.read more >>