how is it possible for the same element to be oxidized in one reaction and reduced in another?

The phenomenon you are referring to is called disproportionation. It occurs when the same element in a compound undergoes both oxidation and reduction simultaneously in different parts of a chemical reaction. To understand how this is possible, let's first review the definitions of oxidation and reduction.

Oxidation is the process in which an atom, ion, or molecule loses electrons, resulting in an increase in its oxidation state. Reduction, on the other hand, is the process where an atom, ion, or molecule gains electrons, leading to a decrease in its oxidation state.

Now, in a disproportionation reaction, there are two reaction steps involving the same element. The first step involves the oxidation of the element, meaning it loses electrons and increases in oxidation state. In the second step, the same element is reduced, gaining electrons and decreasing in oxidation state.

The reason this can happen is due to the presence of different environments or species in the reaction mixture. In one part of the reaction, the element may come into contact with an oxidizing agent, causing it to be oxidized by transferring electrons to the oxidizing agent. In another part of the reaction, the element may encounter a reducing agent that donates electrons to it, thus leading to the reduction of the element.

To further illustrate this concept, here's an example: Consider a reaction where chlorine gas (Cl2) is treated with water (H2O). In this reaction, chlorine gas is both oxidized and reduced. Initially, chlorine gas is an oxidizing agent and oxidizes water to produce hydrochloric acid (HCl) and hypochlorous acid (HClO). In this step, chlorine in Cl2 is reduced to chlorine in HCl.

However, in the second step, hypochlorous acid (HClO) acts as a reducing agent, and it reduces chlorine gas (Cl2) to produce hydrochloric acid (HCl) and oxygen gas (O2). In this step, chlorine in HClO is oxidized to chlorine in Cl2.

So, within the same reaction, the chlorine element undergoes oxidation and reduction.

To summarize, the phenomenon of the same element being oxidized in one reaction and reduced in another is possible through a process called disproportionation. It occurs when different species or environments provide an oxidizing or reducing influence on the element at different stages of the reaction.