University of Central Florida (UCF) CHM2045C Chemistry Fundamentals I Practice Exam 1

The bleaching of hair with hydrogen peroxide is classified as a chemical change due to the alteration of the molecular structure of the pigments present in the hair. When hydrogen peroxide is applied, it reacts chemically with the melanin in the hair, breaking down the pigment molecules responsible for the hair color. This reaction results in the formation of different compounds that do not have the same properties as the original melanin, leading to a change in color.

In a chemical change, the substances involved undergo a transformation into new substances with different compositions and properties. In this case, the original color pigments are decomposed and new substances, lighter in color, are formed.

The process also tends to be irreversible under normal circumstances, which is another key characteristic of chemical changes. While physical changes might involve alterations in appearance without affecting the chemical composition (like freezing or boiling), those do not occur in this bleaching process, reinforcing that it is purely a chemical change.