Which of the following best describes what happens when a substance undergoes a change of state, such as from solid to liquid or liquid to gas?

• A. The atoms within the substance are rearranged to form new molecules.
• B. The substance's chemical composition changes.
• C. The substance's physical properties change, but its chemical identity remains the same.
• D. The substance is converted into a mixture of different compounds.

Answer: (C)

Verified step by step guidance

1. Understand that a change of state (phase change) refers to the transition of a substance between solid, liquid, and gas phases without altering its chemical composition.
2. Recall that during a phase change, the molecules or atoms of the substance gain or lose energy, which affects their physical arrangement and movement but does not break or form chemical bonds.
3. Recognize that because no chemical bonds are broken or formed, the chemical identity of the substance remains unchanged; only physical properties such as shape, volume, and density are affected.
4. Eliminate options that suggest chemical changes, such as rearrangement of atoms into new molecules or conversion into different compounds, since these imply chemical reactions rather than physical changes.
5. Conclude that the best description of a phase change is that the substance's physical properties change, but its chemical identity remains the same.