Which statement best describes the difference between physical and chemical changes?

• A. Physical changes alter the appearance or state of a substance without changing its chemical composition, while chemical changes result in the formation of new substances with different chemical properties.
• B. Physical changes are irreversible, while chemical changes are always reversible.
• C. Physical changes can only occur at high temperatures, whereas chemical changes occur at room temperature.
• D. Physical changes always produce energy, while chemical changes do not involve energy changes.

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the definitions of physical and chemical changes. A physical change affects the form or appearance of a substance but does not alter its chemical composition. Examples include changes in state (solid, liquid, gas) or shape.
2. Step 2: Recognize that a chemical change results in the formation of one or more new substances with different chemical properties and compositions. This often involves breaking and forming chemical bonds.
3. Step 3: Analyze the given statements by comparing them to these definitions. For example, check if the statement about reversibility aligns with the nature of physical and chemical changes (physical changes can be reversible or irreversible, and chemical changes are often irreversible but not always).
4. Step 4: Evaluate the temperature-related statement. Physical changes can occur at various temperatures, not only high temperatures, and chemical changes can occur at room temperature or other temperatures depending on the reaction.
5. Step 5: Consider the energy aspect. Both physical and chemical changes can involve energy changes, but chemical changes typically involve more significant energy changes due to bond breaking and formation.