Question

unit exam - matter and change
which of these changes is an example of a physical change?
polishing a gemstone
bread molds
batter is baked into a cake
sodium and chlorine form table salt

Explanation:

A physical change alters the form or appearance of a substance but does not create a new chemical substance.

• Polishing a gemstone only smooths/reshapes its surface; the gemstone's chemical composition remains unchanged.
• Moldy bread involves microbial growth that creates new chemical compounds (chemical change).
• Baking cake batter causes chemical reactions (like protein denaturation, starch gelatinization) that form a new substance (chemical change).
• Sodium and chlorine reacting to form table salt creates an entirely new chemical compound from two elements (chemical change).

Answer:

polishing a gemstone