Whenever a chemical reaction occurs, the changes that people observe are caused by the creation or loss of certain types of materials. For instance, temperature can generate a chemical reaction. An easy way to recognize a chemical change is to compare the color of the original item with the new one. A number of chemical reactions cause color changes.
Photosynthesis, the chemical reaction that allows plants to use sunlight to manufacture food, plays an important role in color change for tree leaves. During seasons of growth, chlorophyll is constantly produced and broken down, leaving a green color on leaves. Anthocyanins, produced during autumn, turn leaves red. Found in leaves during spring and summer, carotenoids provide the yellow, brown, and orange hues. Since there is a decreased amount of sunlight in autumn and the weather is cooler, all chlorophyll is destroyed. As a result, the anthocyanins and carotenoids are exposed, showing their hues.
Colors and sounds that people observe during a fireworks explosion are a result of several chemical reactions that occur within the fireworks. Oxidizers produce the oxygen gas needed to excite the atoms of compounds that provide the light. All firework colors are a result of metal salts that are heated. For example, strontium carbonate is bright red and copper chloride is blue when burned.
Copper's element color is reddish-brown. When copper reacts with oxygen, water, and carbon dioxide, the brown color turns green. This chemical reaction is referred to as hydrated copper carbonate. On October 28, 1886, the Statue of Liberty had the standard reddish-brown color of copper. Over time the copper plates underwent a chemical reaction. Pennies can also change to a green hue this way.