Which statement describes all chemical changes?

• A. They are always reversible by physical means.
• B. They only change the physical state of a substance.
• C. They do not involve any change in energy.
• D. They result in the formation of one or more new substances with different chemical properties.

Answer: (D)

Verified step by step guidance

1. Understand the definition of a chemical change: it involves a transformation where one or more substances are converted into new substances with different chemical properties.
2. Recognize that chemical changes are different from physical changes, which only affect physical properties like state or appearance without forming new substances.
3. Note that chemical changes often involve energy changes (either absorption or release), so the statement 'They do not involve any change in energy' is incorrect.
4. Acknowledge that chemical changes are generally not reversible by physical means, unlike some physical changes, so the statement about reversibility by physical means is incorrect.
5. Conclude that the correct description of chemical changes is that they result in the formation of new substances with different chemical properties.