Final answer:
A physical change affects the form of a substance without altering its mass or the number of atoms and molecules. During a chemical change, while the properties and composition may change, the mass and number of atoms are conserved due to the Law of Conservation of Mass.
Step-by-step explanation:
When matter undergoes a physical change, such as melting or freezing, its form may change, but the amount of matter, or mass, remains constant. The identity of the substance does not change because the molecules do not break apart or form new compounds. During a physical change, the number of molecules and atoms stays the same.
In contrast, a chemical change involves the rearrangement of atoms to create new substances with different properties. Even though the substances' properties change, no atoms are lost or gained in the process. The Law of Conservation of Mass states that atoms are conserved, meaning the total mass remains the same before and after a chemical reaction.
It is important to note while the mass and amount of matter remain unaffected by both physical and chemical changes, the properties and compositional structure may vary significantly in the case of a chemical change.