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Chapter 1: Problem 6

If you place a glass rod over a burning candle, the glass appears to turn black. What is happening to each of the following (physical change, chemical change, both, or neither) as the candle burns? Explain each answer. a. the wax b. the wick c. the glass rod

Short Answer

Expert verified
a. The wax undergoes both physical and chemical changes. It melts due to heat (physical change) and reacts with oxygen to produce carbon dioxide and water vapor (chemical change). b. The wick undergoes both physical and chemical changes. It absorbs the liquid wax (physical change) and reacts with oxygen releasing carbon dioxide and water vapor (chemical change). c. The glass rod undergoes a physical change. Its appearance turns black due to the deposition of soot, which can be cleaned off, but there is no chemical change.

Step by step solution

01

a. The wax

When the candle burns, the wax melts due to heat, which is a physical change because it only alters the state of the wax from solid to liquid. However, the heat from the flame also causes the wax molecules to react with oxygen, producing carbon dioxide and water vapor, which is a chemical change. So, the wax undergoes both physical and chemical changes.
02

b. The wick

The wick absorbs the liquid wax and provides fuel to continue the burning process, which is a physical change as it only takes up the wax. However, as the wick burns, it reacts with oxygen, and the combustion results in the release of carbon dioxide and water vapor, which is a chemical change. Therefore, the wick undergoes both physical and chemical changes.
03

c. The glass rod

As for the glass rod, it undergoes a physical change when it is placed over the burning candle. The glass appears to turn black due to the deposition of soot (unburned carbon particles) from the burning process on its surface. This change is only a temporary alteration of appearance and can be cleaned off, so the glass undergoes a physical change but no chemical change.

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