The Hill Reaction takes place when chloroplasts or chloroplast fragments in light split water in the absence of carbon dioxide. This reaction occurs when electrons from water transfer to an electron acceptor, reducing the acceptor.
Robin Hill and R. Scarisbrick first observed the Hill Reaction in the late 1930s. The team found it when they carried out an experiment in which isolated chloroplasts released oxygen in the light when given an acceptor for the electrons being removed from the oxygen.
To create this reaction, students and scientists often use dichlorophenol indophenol (DCPIP) as the acceptor. In many schools, students do experiments to measure the rate of the Hill Reaction.