Question

which statement is not evidence that a new substance has formed during a chemical reaction?
gas is produced
temperature changes
precipitate forms
substance melts

Explanation:

To determine which is not evidence of a new substance in a chemical reaction, we analyze each option:

• Gas production (like in acid - metal reactions) shows a new substance (gas) is formed.
• Temperature changes (exothermic/endothermic reactions) indicate energy changes from new substance formation.
• Precipitate formation (e.g., in double - displacement reactions) means a new insoluble substance is made.
• Substance melting is a physical change (phase change, like ice melting to water) where the substance's identity (H₂O) remains the same, so no new substance is formed.

Answer:

Substance melts