When iron reacts with vinegar, the metal rusts and causes an exothermic chemical reaction, which produces heat. This is commonly reproduced in experiments with either an iron nail or steel wool and vinegar.
The vinegar removes the iron's protective coating, causing the metal to rust. The acidity within the removed protective coating facilitates the rusting process. The oxygen then mixes with the iron, which is what causes the resulting exothermic reaction. When iron rusts, four iron atoms react with three oxygen molecules to form two rust molecules. The experiment using steel wool or an iron nail and vinegar can be performed in 15 minutes.