Question

For the galvanic cell reaction, expressed below using shorthand notation, what half-reaction occurs at the anode? 1. Mg(s) Mg2+(aq) 2. Cd2+(aq) Cd(s) A) Mg(s) → Mg2+(aq) + 2 e- B) Mg2+(aq) + 2 e- → Mg(s) C) Cd(s) → Cd2+(aq) + 2 e- D) Cd2+(aq) + 2 e- → Cd(s)

Answer 1

Answer : The half-cell reaction occurs at the anode is,

(B) $Mg(s)\rightarrow Mg^{2+}(aq)+2e^-$

Explanation :

Galvanic cell : It is defined as a device which is used for the conversion of the chemical energy produces in a redox reaction into the electrical energy. It is also known as the voltaic cell or electrochemical cell.

In the galvanic cell, the oxidation occurs at an anode which is a negative electrode and the reduction occurs at the cathode which is a positive electrode.

Redox reaction or Oxidation-reduction reaction : It is defined as the reaction in which the oxidation and reduction reaction takes place simultaneously.

Oxidation reaction : It is defined as the reaction in which a substance looses its electrons. In this, oxidation state of an element increases. Or we can say that in oxidation, the loss of electrons takes place.

Reduction reaction : It is defined as the reaction in which a substance gains electrons. In this, oxidation state of an element decreases. Or we can say that in reduction, the gain of electrons takes place.

The given two-half reactions are:

(1)  $Mg(s)\rightarrow Mg^{2+}(aq)+2e^-$

(2) $Cd^{2+}(aq)+2e^-\rightarrow Cd(s)$

According to the galvanic cell, the half-cell reaction (1) shows oxidation reaction so, it occurs at anode and the half-cell reaction (2) shows reduction  reaction so, it occurs at cathode.

Hence, the half-cell reaction occurs at the anode is,

$Mg(s)\rightarrow Mg^{2+}(aq)+2e^-$