Final answer:
Redox reactions involve changes in oxidation numbers indicating electron transfer. The redox status of a species depends on whether oxidation (loss of electrons) or reduction (gain of electrons) has occurred. By determining oxidation numbers, the oxidizing and reducing agents in a reaction can be identified.
Step-by-step explanation:
Oxidation-reduction (redox) reactions are chemical reactions involving a transfer of electrons between two species. An increase in oxidation number indicates oxidation, while a decrease indicates reduction. To identify a redox reaction, one must look at the change in oxidation numbers of the elements in the reactants and products.
In the reaction Sr + SO3 → SrSO3, strontium (Sr) is oxidized as its oxidation number goes from 0 in elemental form to +2 in the compound, making it the reducing agent. The sulfur (S) in SO3 is reduced, its oxidation number remains +4, indicating that no redox reaction has occurred in this case, as there is no change in oxidation state of sulfur.
For 2KrF2 + 2H2O → 2Kr + 4HF + O2, the krypton (Kr) goes from an oxidation state of +1 in KrF2 to 0 in Kr, showing it is reduced and thus acting as an oxidizing agent. Oxygen (O) is oxidized from -2 in H2O to 0 in O2, making it the reducing agent. This is an example of a true redox reaction.
In another example, SO3 + SCl2 → SOCl2 + SO2, both sulfur compounds undergo changes in their oxidation numbers; therefore, this is also a redox reaction. Identifying the oxidant and reductant requires assigning oxidation numbers and observing which species are oxidized and which are reduced.