Final answer:
In a redox reaction, one substance is oxidized and another substance is reduced. The substance that undergoes oxidation has an increase in oxidation number, while the substance that undergoes reduction has a decrease in oxidation number. The reducing agent is the substance that donates electrons, causing another substance to be reduced, while the oxidizing agent is the substance that accepts electrons, causing another substance to be oxidized.
Step-by-step explanation:
In a redox reaction, one substance is oxidized (loses electrons) and another substance is reduced (gains electrons). To identify the substance that is oxidized, we look at the change in oxidation number. The substance whose oxidation number increases is the substance that is oxidized. To identify the substance that is reduced, we look at the change in oxidation number. The substance whose oxidation number decreases is the substance that is reduced.
In the reaction Zn + HCl → H₂ + ZnCl₂, Zn is oxidized because its oxidation number increases from 0 to +2. HCl is reduced because the H in HCl goes from +1 to 0 in H₂.
The reducing agent is the substance that causes another substance to be reduced. In this reaction, Zn is the reducing agent because it donates electrons to HCl, causing it to be reduced.
The oxidizing agent is the substance that causes another substance to be oxidized. In this reaction, HCl is the oxidizing agent because it accepts electrons from Zn, causing it to be oxidized.