A process by which chemical bonds can be broken or made.

• A. Chemical reaction
• B. Physical change
• C. Phase transition
• D. Separation

Answer: (A)

Bond breaking and bond forming define a chemical reaction. When substances react, the existing bonds in the reactants are broken and new bonds are formed to make different substances with new properties. This is different from a physical change, like melting or boiling, where the covalent bonds inside molecules remain intact and only the arrangement or state of the molecules changes. Phase transitions involve changing the state due to energy changes but don’t create new substances, and separation is about dividing components without altering the bonds within the molecules. For instance, burning methane breaks chemical bonds and forms new ones to yield carbon dioxide and water.