Question

which of the following best describes a chemical reaction? a) atoms rearrange to form new substances b) molecules move faster when heated c) substances mix without changing d) matter disappears
substances mix without changing
atoms rearrange to form new substances
matter disappears
molecules move faster when heated

Explanation:

• Option A: In a chemical reaction, bonds between atoms break and re - form, leading to the rearrangement of atoms to create new substances with different properties. This is the core definition of a chemical reaction.
• Option B: Molecules moving faster when heated is a description of the effect of heat on molecular motion, which is related to physical changes (like temperature - related changes in state or kinetic energy of molecules in a substance) rather than a chemical reaction.
• Option C: Substances mixing without changing is a physical mixture (like mixing salt and sand), where no new substance is formed, so it is not a chemical reaction.
• Option D: According to the law of conservation of mass, matter cannot disappear in a chemical reaction. The atoms are just rearranged, and the total mass of reactants and products remains the same.

Answer:

A) Atoms rearrange to form new substances