Question

A half cell reaction is one which:
A.Involves only half a mole of electrolyte
B.Goes only halfway to completion
C.Takes place at one electrode
D.Consumes half a unit of electricity

Answer 1

An oxidation reaction in which the electrons are lost or a reduction reaction in which electrons are gained is known as a half cell reaction. The half cell reaction occurs in an electrochemical cell.

Complete step by step answer:
A half cell reaction can be an oxidation reaction or it can be a reduction reaction. In the oxidation reaction, electrons are lost and in the reduction reaction, electrons are gained.
The half cell reaction occurs in an electrochemical cell at the electrodes.
At anode, oxidation reaction occurs which is known as oxidation half reaction. Ant at cathode, reduction reaction occurs, which is known as reduction half reaction.
The two half cell reactions are collectively known as a redox reaction.
Thus, the half cell reaction is one which takes place at one electrode.
The half cell reactions can be reversed. The number of electrons lost and gained in the half cell reactions remains constant.
Therefore, the correct option is C.

Note:
The example of a half cell reaction at anode is as follows: ${\text{Zn}}\left( {\text{s}} \right) \to {\text{Z}}{{\text{n}}^{2 + }}\left( {{\text{aq}}} \right) + 2{e^ - }$. In the reaction, the zinc metal loses 2 electrons and forms ${\text{Z}}{{\text{n}}^{2 + }}$ ion. The electrons are lost, thus, the half cell reaction at anode is an oxidation half reaction.
The example of a half cell reaction at cathode is as follows: ${\text{C}}{{\text{u}}^{2 + }}\left( {{\text{aq}}} \right) + 2{e^ - } \to {\text{Cu}}\left( {\text{s}} \right)$. In the reaction, the ${\text{C}}{{\text{u}}^{2 + }}$ ion gains 2 electrons and forms copper metal. The electrons are gained, thus, the half cell reaction at cathode is a reduction half reaction.
In an oxidation half reaction, the electrons are products whereas in a reduction half reaction, the electrons are reactants.