The chemical equation of film exposure

AgBr is photosensitive and is often used in photographic films.

The film is coated with a layer of gelatin containing fine silver bromide. During photography, light of different strengths shines on the film. This causes AgBr to decompose to varying degrees on the film. The decomposition product bromine combines with gelatin and silver becomes extremely fine silver nuclei and precipitates on the film. The more AgBr decomposes in the part of the film that is sensitive to light, the darker the part will be.

The chemical equation of film exposure is:

2AgBr=2Ag+Br2 (condition is light)

The silver bromide that did not participate in the reaction is dissolved during fixation to form the transparent part of the film .