How can you identify an oxidation-reduction (redox) reaction?

An oxidation-reduction (redox) reaction is characterized primarily by changes in oxidation states and the transfer of electrons between substances. During these reactions, one species loses electrons (is oxidized) while another gains electrons (is reduced). By examining the oxidation states of the elements in the reactants and products, you can determine which elements have been oxidized and which have been reduced.

For example, in the reaction between hydrogen and oxygen to form water, hydrogen goes from an oxidation state of 0 in H2 to +1 in H2O, indicating oxidation, while oxygen goes from 0 in O2 to -2 in H2O, indicating reduction. This is a clear indication of a redox process through the analysis of changes in oxidation states.

Changes in temperature, the amount of reactants used, and the types of products formed can be associated with chemical reactions in general but do not specifically indicate the occurrence of a redox reaction. Such factors may be relevant in studying reaction conditions or thermodynamics but they do not provide the same direct insight into electron transfer processes as changes in oxidation states do.