The EMF of the standard weston cadmium cell
Cd (12.5%) in Hg | 3 CdSO4, 8H2O (solid) | standard solution of CdSO4 | Hg2SO4 (s) | Hg is 1.0180 volts at 25°C and the temperature coefficient of the cell emf, \(\left(\frac{\delta E}{\delta T}\right)_P\) = \(-4.0 × 10^{-5}\text{ V deg}^{-1}\). Calculate \(\Delta G\), \(\Delta H\) and \(\Delta S\) for the reaction in the cell when n = 2.
Answer & explanation
Correct answer: option 1
Given,
\(\left(\frac{\delta E}{\delta T}\right)_P\) = \(-4.0 x 10^{-5}\text{ V deg}^{-1}\)
\(n = 2\)
\(E^0_{cell} = 1.0181V\)
We know,
\(\Delta G^0 = −2FE^0_{cell}\)
or, \(\Delta G^0 = −2 × 96500 × 1.018\)
or, \(\Delta G^0 = −196474 J\)
or, \(\Delta G^0 = −196.5 kJ\)
\(\Delta S^0 = nF\left(\frac{dE}{dT}\right)\)
or, \(\Delta S^0 = −2 × 96500 × 4.0 × 10^{-5}\)
or, \(\Delta S^0 = −7.72 J/deg\)
\(\Delta H^0 =nF\left(T\left(\frac{dE}{dT}\right)_P − E^0_{cell} \right) = 198.8 kJ\)