QQuestionChemistry
QuestionChemistry
Why is the evaporation of water a physical change and not a chemical change?
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Answer
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Step 1:I'll solve this problem step by step, explaining the key differences between physical and chemical changes with respect to water evaporation.
Step 2:: Define Physical Change
A physical change is a transformation that alters the physical properties of a substance without changing its chemical composition. In a physical change: - The molecular structure remains the same - No new substances are formed - The change can be reversed easily - Only physical properties like state, shape, or size are altered
Step 3:: Examine Water Evaporation
H_{2}O_{(liquid)} \rightarrow H_{2}O_{(gas)}
During evaporation, water transitions from a liquid to a gas (water vapor) state. Let's analyze the key characteristics:
Step 4:: Chemical Composition Remains Unchanged
- The molecular formula $$H_{2}O$$ remains identical before and after evaporation
- No new chemical bonds are formed or broken - The hydrogen and oxygen atoms remain connected in the same configuration
Step 5:: Reversibility
- Water vapor can be easily converted back to liquid water through condensation - This demonstrates the substance's fundamental chemical identity remains constant
Step 6:: Physical Property Changes
- State changes from liquid to gas - Molecules gain kinetic energy and spread out - Density decreases - Volume increases
Final Answer
Evaporation is a physical change because the chemical composition of water remains unchanged, the molecular structure is preserved, and the transformation can be easily reversed.
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