Touching a 9V battery to fine steel wool creates a striking demonstration of electrochemistry and thermodynamics in action. Steel wool is made of thin strands of iron with a very high surface-area-to-volume ratio. When the battery terminals contact the fibers, they complete a circuit. Current flows through the resistive metal strands, producing Joule heating (I²R heating). Because the fibers are so thin, they heat up quickly. At elevated temperatures, iron reacts with oxygen in the air. This is an oxidation reaction: iron atoms lose electrons and combine with oxygen to form iron oxides (primarily Fe₂O₃ and Fe₃O₄). The process is exothermic, meaning it releases heat, which sustains and propagates the glowing reaction along adjacent fibers. What looks like “burning” is actually rapid oxidation accelerated by electrical heating. The glow you see is incandescence—light emitted due to high temperature—not a flame driven by a volatile fuel. Key factors that control the reaction: * Surfa...