Why can chemical changes often not be reversed?

• A. Because new substances with different chemical properties are formed during a chemical change.
• B. Because the physical state of the substance changes, but its chemical composition remains the same.
• C. Because chemical changes only involve changes in temperature and pressure.
• D. Because chemical changes are always caused by mixing substances physically.

Answer: (A)

Verified step by step guidance

1. Understand the difference between physical and chemical changes: Physical changes affect the form or state of a substance without altering its chemical composition, while chemical changes result in the formation of new substances with different chemical properties.
2. Recognize that during a chemical change, bonds between atoms are broken and new bonds are formed, leading to substances that have different molecular structures and properties than the original substances.
3. Because new substances are formed, reversing the chemical change would require breaking these new bonds and reforming the original substances, which is often difficult or impossible under normal conditions.
4. In contrast, physical changes are usually reversible because the chemical composition remains unchanged, so returning to the original state does not require altering chemical bonds.
5. Therefore, chemical changes often cannot be reversed because the process creates new substances with different chemical properties, making the original substances no longer present in their initial form.