What happened to the temperature in the last experiment? And how did the steel wool look at the end? You should have seen that the temperature went up by several degrees, and that the steel wool looked rusty after the experiment was done. What happened?
First of all, what exactly is steel wool? Is it the fleece from metallic sheep? Of course not. Steel wool is just very thin wires made of iron that is sold in clumps that looks something like sheep's wool. It is often used instead of sandpaper for removing paint or smoothing surfaces.
So, where did the heat come from? When iron comes in contact with the oxygen (O2) and water (H2O) in air, a chemical reaction called oxidation occurs. Rust is actually a mixture of several compounds of iron, oxygen, and hydrogen, with names like iron oxide and iron hydroxide. Do you remember learning about thermal energy in "Where Does Heat Come From?"? We said that a wood fire feels hot because the thermal energy of the wood was higher than that of the ashes and other material left over from the fire. The same thing applies to the iron. The thermal energy of rust is lower than that of the original iron, and you feel the energy lost as heat.
But why didn't the steel wool rust before you put it into the jar? Normally, steel wool is coated with oil or some other material that protects it from air. The vinegar you rinsed the steel wool with took the coating away, and the bare iron was exposed. So, the vinegar wasn't actually involved in the reaction, but it did allow the reaction to happen.
If you go to the drugstore, you can actually find a product that uses the oxidation of iron to generate heat! ThermaCare heat wraps contain iron (and some other chemicals) that react with air and produce warmth that helps relieve the pain of arthritis and sore muscles.
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