Question

How do you write the equations for half-cell reactions?

Answer 1

Half-cell reactions are basically the oxidation or reduction reaction which takes place in a cell. These reactions may account for oxidation of atoms by increase in oxidation or they may account for reduction reactions by decrease in oxidation state. We will take an example to understand these half-cell reactions.

Complete Step By Step Answer:
The redox reactions are those reactions which comprises both oxidation and reduction reactions. These oxidation and reduction reactions when written separately are known as half-cell reactions. Whenever there is an increase in oxidation state of an element then it is taking place at anode. Also when there is decrease in oxidation state of an element then it takes place in the cathode. Therefore we can say that oxidation takes place at anode and reduction takes place at cathode.
For example: Oxidation of copper
The oxidation of copper will take place at anode and can be represented as:
$Cu(s){\text{ }} \to {\text{ }}C{u^{2 + }}(aq.){\text{ }} + {\text{ 2e}}$
Thus copper loses two electrons and thus the oxidation state of copper increases and it will form $C{u^{2 + }}$ . Hence it is known as half-cell oxidation reaction. Similarly we can write half-cell reduction reaction for copper as:
$C{u^{2 + }}(aq.){\text{ }} + {\text{ 2e }} \to {\text{ }}Cu(s)$
Here copper ions accept two electrons and form a copper element. Thus it is known as half-cell reduction reaction.

Note:
The half-cell reactions are basically the reaction which takes place at cathode and anode reactively. If it is taking place at anode then it is known as half-cell oxidation reaction. When it takes place at cathode it is known as half-cell reduction reaction. With the help of half-cell reactions we can write the reaction for the whole cell which will be a redox reaction.