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EMF

The standard ...

Question

The standard electrode potential $E^{⊖}$ and its temperature coefficient $(\frac{d E^{⊖}}{d T})$ for a cell are $2 V$ and $- 5 \times 10^{- 4} V K^{- 1}$ at $300 K$ respectively. The cell reaction is
$Z n (s) + C u^{2 +} (a q) \to Z n^{2 +} (a q + C u (s)$
The standard reaction enthalpy $(△_{r} H^{⊖})$ at $300 K$ in $k J m o l^{- 1}$ is:
$[U s e R = 8 j K^{- 1} m o l^{- 1}$ and $F = 96, 000 C m o l^{- 1}]$

- 412.8

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- 384.0

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206.4

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192.0

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Solution

The correct option is A $- 412.8$
We have,
$Δ G = Δ H - Δ S$ ---------(1)
Also,
$Δ G = - n F E_{c e l l} = - 2 \times 96500 \times 2 = - 4 \times 96500$
Now, $Δ S = n F \frac{d E}{d T} = 2 \times 96500 \times (- 5 \times 10^{- 4}) = 96.5 J$
Now from equation (1)
$Δ H = Δ G + T Δ S = - 4 \times 96500 + 298 \times (- 96.5) \approx - 412.8$

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