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Chapter 1: Problem 22

A match is lit to light a candle. The following observations are made: (a) The candle burns. (b) Some wax melts. (c) Melted wax solidifies on the candleholder. (d) Soot (carbon) is produced by the burning of the match and the candle. Which of these occurrences are due to physical changes, and which are due to chemical changes?

Short Answer

Expert verified
Physical changes: (b) Wax melting and (c) Melted wax solidifying on the candleholder. Chemical changes: (a) Candle burning and (d) Soot (carbon) production.

Step by step solution

01

Observation (a): Candle Burns

When the candle burns, it is a chemical reaction taking place. The wax in the candle combines with the oxygen in the air to produce carbon dioxide, water, and heat. This is a process known as combustion. Since this process involves a change in the substance's chemical composition, it is a chemical change.
02

Observation (b): Wax Melts

When wax melts, its state changes from solid to liquid, but its underlying chemical composition remains the same. In this case, the molecules of wax are just moving more freely, rather than changing their nature. This is a physical change, as there is no change in the chemical composition of the substance.
03

Observation (c): Melted Wax Solidifies on the Candleholder

When the melted wax cools down and solidifies, it changes from its liquid state back to a solid state. Again, this does not involve any chemical reaction, as the composition of the wax remains the same. Therefore, this observation represents a physical change.
04

Observation (d): Soot (Carbon) is Produced

As the match and the candle burn, soot (carbon) is produced, which is a result of incomplete combustion. In this process, the chemical composition of the original substances (match, candle, and oxygen) is changed, and new substances (soot, carbon dioxide, and water) are formed. Hence, this observation represents a chemical change. In conclusion: Physical changes: (b) Some wax melts, and (c) Melted wax solidifies on the candleholder. Chemical changes: (a) The candle burns, and (d) Soot (carbon) is produced.

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Most popular questions from this chapter

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