Question

The standard reduction potentials for two half-cell reactions are given below.
$Cd ^{2+}( aq )+2 e^{-} \rightarrow Cd ( s ) ; E ^{\circ}=-0.40 V$
$Ag ^{+}( aq )+e^{-} \rightarrow Ag ( s ), E ^{\circ}=0.80 V$
The standard free energy change for the reaction
$2 Ag ^{+}( aq )+ Cd ( s ) \rightarrow 2 Ag ( s )+ Cd ^{2+}( aq )$ is given by

• A. $115.8 \,kJ$
• B. $-115.8 \, kJ$
• C. $-231.6 \, kJ$
• D. $231.6 \,kJ$

Answer 1

Answer: (C)

$2 Ag ^{+}( aq )+2 e^{-} \rightarrow 2 Ag ( s ) ; E ^{\circ}=0.80\, V$
$Cd ( s ) \rightarrow Cd ^{2+}( aq )+2 e^{-} ; E ^{\circ}=0.40\, V$
$2 Ag ^{+}( aq )+ Cd ( s ) \rightarrow 2 Ag ( s )+ Cd ^{2+}( aq ) ; E ^{\circ}=1.20\, V$
$\Delta G =- nFE ^{\circ}=-2 \times 96500 \times 1.20=-231.6 \, kJ$