Pennies become dull or change color with prolonged exposure to air because they are made of copper, which reacts to the presence of oxygen by forming copper oxide. Copper oxide is blue-green and has a common name of "ver...
When copper is heated, it decomposes to form copper oxide and carbon dioxide. It is an endothermic reaction, which means that it absorbs heat. When heated, copper is easily bent or molded into shapes.