Which is an example of a chemical change?

• A. Ice melting
• B. Dissolving sugar in water
• C. Wood burning
• D. Sublimation of dry ice

Answer: (C)

A chemical change is when a substance is transformed into new substances with different identities, often accompanied by energy changes and the formation of new products. Wood burning demonstrates this because the polymers in wood react with oxygen in the air to form new substances like carbon dioxide, water, and ash. Bonds in the wood are broken and new bonds form in the products, and energy is released as heat and light. This isn’t just a rearrangement of matter; the chemical composition changes.

Ice melting, dissolving sugar in water, and the sublimation of dry ice are all physical changes. Melting ice changes the state of water but not its composition. Dissolving sugar distributes sugar molecules in water without creating a new substance. Subliming dry ice changes its phase from solid to gas but remains CO2, so no chemical transformation occurs.