Q. The standard emf of the cell, $Cd\ (s)\ |\ {CdCl}_{2}\ (aq)\ (0.1\ M)\ ||\ AgCl\ (s)\ |\ Ag\ (s)$ In which the cell reaction is $Cd\ (s) + \ 2AgCl\ (s)$ $\rightarrow \ 2\ Ag\ (s)\ + \ {Cd}^{2 +}\ (aq)\ + \ {2Cl}^{-}\ (aq)\$ is 0.6915 V at 0℃ and 0.6753 V at 25 ℃ . The enthalpy change of the reaction at 25℃ is

A) -176 kJ
B) -234.7 kJ
C) +123.5 kJ
D) -167.26kJ
Explanation

(d)
The cell reaction is
Cd (s) + 2AgCl (s) → 2 Ag (s) + ${Cd}^{2 +}$ (aq) + ${2Cl}^{-}$ (aq)
$E_{1}$ = 0.6915 V at 0℃
$E_{2}$ = 0.6753 V at 25℃
Now, $\frac{\partial\ E_{cell}}{\partial\ T}$ = $\frac{E_{2} - \ E_{1}}{T_{2} - \ T_{1}}$
= $\frac{0.6753 - 0.6915}{298 - 273}$
= - 6.48 × $10^{- 4}$
△S =nF $\left\lbrack \frac{\partial\ E_{cell}}{\partial\ T} \right\rbrack$
Now, we put the value
△S = 2 × 96500 (- 6.48 × $10^{- 4}$ ) = - 125.064
We know that,
△G $= \ - nFE_{cell}$
= - 2 × 96500 × 0.6753
= - 1.303 × $10^{5}$
As, △G = △H - T△S
For calculating △H = △G + T△S
= - 1.303 × $10^{5}$ + 298 (- 125.064 kJ)
△H = - 1.6726 × $10^{5}$ J
= - 167.26 kJ

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.