What type of reactions supply energy in chemotrophs?

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Chemotrophs obtain energy from chemical reactions that involve oxidation–reduction (redox) changes. In these organisms, an electron donor is oxidized while an electron acceptor is reduced, and the energy released by that electron transfer is captured to make ATP—often via a proton motive force generated by the electron transport chain, and sometimes directly through substrate-level phosphorylation. The driving force is the redox potential difference between donor and acceptor, not light capture or simple bond-breaking. For example, respiration transfers electrons to external acceptors like oxygen, producing energy; fermentation uses internal redox steps but yields less energy and relies more on substrate-level phosphorylation. So the energy-supplying reactions in chemotrophs are redox reactions involving chemical compounds.