Which of the following statements correctly describes the chemical property involved in the evaporation of methanol at 25.0 °C: CH3OH(l) → CH3OH(g)?

• A. Evaporation of methanol is a physical change because no new substances are formed.
• B. Evaporation of methanol is a chemical change because the chemical composition of methanol changes.
• C. Evaporation of methanol involves breaking covalent bonds within the CH3OH molecule.
• D. Evaporation of methanol results in the formation of methanal (CH2O) as a product.

Answer: (A)

Verified step by step guidance

1. Understand the difference between physical and chemical changes: A physical change affects the state or appearance of a substance without altering its chemical composition, while a chemical change results in the formation of new substances with different chemical properties.
2. Analyze the process of evaporation: Evaporation is the transition of a substance from the liquid phase to the gas phase, which involves overcoming intermolecular forces but does not break covalent bonds within the molecules themselves.
3. Apply this to methanol (CH3OH): When methanol evaporates, the molecules move from liquid to gas, but the chemical formula CH3OH remains unchanged, indicating no new substances are formed.
4. Evaluate the given statements: Since evaporation does not change the chemical composition or create new substances, it is classified as a physical change, not a chemical change.
5. Conclude that evaporation of methanol does not involve breaking covalent bonds or forming methanal (CH2O), so the correct description is that evaporation is a physical change because no new substances are formed.