Chemicals can have similar formulas and names but different properties and uses. Hydrogen cyanide (HCN) and methyl cyanide (MeCN) are similar in formula and name, but behave differently. Inhalation of hydrogen cyanide kills, but methyl cyanide is a solvent, and poisoning by it is rare. Likewise, hydrogen peroxide and benzoyl peroxide have similar names and formulas, but find different applications.

The chemical formula of hydrogen peroxide (H2O2) is very similar to water (H2O). Benzoyl peroxide contains a phenyl group, which can be symbolized Ph-. We can write benzoyl peroxide as (Ph-CO)2O2.

Hydrogen peroxide splits and loses oxygen to form water:

2 H2O2 --> 2 H2O + O2.

Hydrogen peroxide is used for minor medical cosmetic purposes, and in industrial bleaching applications.

Benzoyl peroxide has the formula (Ph-CO)2O2. Benzoyl peroxide can lose oxygen in the presence of water to form benzoic acid:

2 (PhCO)2O2 + 2 H2O --> 4 PhCOOH + 3 O2.

Unlike hydrogen peroxide, benzoyl peroxide is not water-soluble and forms a film.

There is an additional reaction making benzoyl peroxide useful for other purposes. Apart from moisture, in the presence of heat, benzoyl peroxide can split to form two free radicals:

(PhCO)2O2 + heat --> 2 PhCOO?

This heat-driven reaction makes benzoyl peroxide useful to the chemical industry.

Hydrogen peroxide is useful where film-formation is not an important characteristic, such as bleaching hair and disinfecting small wounds. It is an important bleaching agent in paper manufacture.

Benzoyl peroxide forms a film, making it useful in whitening teeth and treating acne. It is useful as a free-radical initiator in polymer manufacture and other organic chemical processes.