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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
The wax undergoes both physical (melting) and chemical (combustion) changes. The wick primarily undergoes a chemical change (combustion) as it burns. The glass rod undergoes a physical change, with soot particles adhering to its surface, making it appear black.

Step by step solution

01

A. Analyzing the Wax

When a candle burns, the wax melts due to heat, which is a physical change. As the liquid wax reaches the flame, it undergoes combustion, a reaction with oxygen that releases heat and light. This combustion process breaks down the wax's chemical bonds and produces new molecules, such as carbon dioxide and water. Thus, the wax undergoes a chemical change as well. So, in the case of the wax, both physical and chemical changes are happening.
02

B. Analyzing the Wick

The wick is made from a material that absorbs the liquid wax and transports it upwards to the flame. The wick undergoes combustion, much like the wax. As it burns, the chemical bonds in the wick are broken down, and new molecules are formed. The wick becomes shorter and eventually gets consumed. This change in the wick is primarily driven by a chemical change (combustion).
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C. Analyzing the Glass Rod

When the glass rod is placed over the burning candle, it does not undergo any chemical change. Instead, it gets covered in soot, which is a physical change. Soot consists of tiny particles of carbon that form as the candle burns. The soot particles adhere to the glass rod's surface, making it appear black. Since no chemical bonds are broken or formed in the glass rod, it undergoes a physical change.

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