What is a chemical reaction?

• A. A process that creates energy but not new substances.
• B. A process that only rearranges the atoms without changing substances.
• C. A process that forms new substances called products from starting substances called reactants.
• D. A reaction that occurs only in gas form.

Answer: (C)

A chemical reaction is a process in which reactants transform into new substances called products. This happens because chemical bonds are broken and new bonds form, giving substances with different properties from the starting materials. Energy may be released or absorbed during the reaction, but the defining feature is the creation of new substances, not just a change of state or a rearrangement of atoms. It’s different from a physical change, where the substance remains the same chemically, such as ice melting or sugar dissolving. A simple example is hydrogen reacting with oxygen to form water.