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Which of the following is an example of a chemical change?
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1. Intro to General Chemistry
Physical & Chemical Changes
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Which of the following best describes what happens to water when it freezes?
A
Water undergoes a chemical change, forming a new substance with different chemical properties.
B
Water decomposes into hydrogen and oxygen gases.
C
Water undergoes a physical change, turning from a liquid to a solid without altering its chemical composition.
D
Water evaporates and becomes a gas.
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Understand the difference between physical and chemical changes: A physical change affects the form of a substance but not its chemical composition, while a chemical change results in the formation of new substances with different chemical properties.
Recall the process of freezing water: When water freezes, it changes from liquid to solid (ice) due to a decrease in temperature, but the molecular structure of H\_2O remains the same.
Analyze the options given: Freezing does not break water molecules into hydrogen and oxygen gases, so decomposition is incorrect; it also does not involve evaporation, which is a phase change from liquid to gas.
Conclude that freezing water is a physical change because the chemical identity of water remains unchanged, only its physical state changes from liquid to solid.
Therefore, the best description is that water undergoes a physical change, turning from a liquid to a solid without altering its chemical composition.
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