Question

(sc8.p9.2) mrs. flores asked her class to describe a chemical change. which of the following descriptions is correct? a chemical change occurs whenever a substance is undergoing a change in its state. a chemical change produces new substances with different properties than the original substances. a chemical change does not affect the composition of a substance. a chemical change can occur without changing the molecules of the substances.

Explanation:

A chemical change involves the transformation of substances at the molecular level. When a chemical change occurs, the reactant molecules break apart and recombine to form new product molecules with different properties than the original substances. For example, in the combustion of hydrogen (\(2H_2 + O_2
ightarrow 2H_2O\)), hydrogen and oxygen (reactants) combine to form water (product). The properties of water (e.g., being a liquid at room - temperature, ability to extinguish fires in some cases) are different from those of hydrogen (a highly flammable gas) and oxygen (a gas that supports combustion).

• The first option ("A chemical change occurs whenever a substance is undergoing a change in its state") describes a physical change. Physical changes, like melting (solid to liquid) or vaporization (liquid to gas), involve changes in state but not in the chemical composition of the substance.
• The third option ("A chemical change does not affect the composition of a substance") is incorrect. As mentioned above, chemical changes do change the composition.
• The fourth option ("A chemical change can occur without changing the molecules of the substances") is also wrong. Chemical changes are fundamentally about molecular - level changes.

Answer:

A chemical change produces new substances with different properties than the original substances.