Which statement describes a chemical change?

Which statement describes a chemical change?

• A. When a substance is melted
• B. When a substance changes phase only
• C. When a substance is dissolved
• D. When a substance transforms into a different substance during a reaction

Answer: (D)

Chemical changes involve forming new substances with different identities, as bonds are broken and new ones are formed during a reaction. The statement describes a substance becoming a different substance as a reaction occurs, which is exactly what defines a chemical change. For example, burning methane yields carbon dioxide and water, and iron reacting with oxygen forms iron oxide—new substances with different properties. In contrast, melting a substance is a physical change: the material remains the same substance, just in a different phase, so its identity and composition don’t change. Changing phase only refers to transitions like solid to liquid or liquid to gas, which don’t produce new substances. Dissolving a substance is typically a physical process where the molecules remain the same chemicals, unless a chemical reaction occurs after dissolution. So, the description of transforming into a different substance during a reaction best captures the idea of a chemical change.

Chemical changes involve forming new substances with different identities, as bonds are broken and new ones are formed during a reaction. The statement describes a substance becoming a different substance as a reaction occurs, which is exactly what defines a chemical change. For example, burning methane yields carbon dioxide and water, and iron reacting with oxygen forms iron oxide—new substances with different properties.

In contrast, melting a substance is a physical change: the material remains the same substance, just in a different phase, so its identity and composition don’t change. Changing phase only refers to transitions like solid to liquid or liquid to gas, which don’t produce new substances. Dissolving a substance is typically a physical process where the molecules remain the same chemicals, unless a chemical reaction occurs after dissolution.

So, the description of transforming into a different substance during a reaction best captures the idea of a chemical change.