Question

Predict which of the following reactions would proceed spontaneously at 298 K ? Take $E_{F{e}^{2+}/Fe}^0=-0.44V$

• A. $Co\left(s\right)+F{e}^{2+}\left(aq\right)\to \left(C{o}^{2+}\right(aq)+Fe(s)$
  $E_{C{o}^{+2}/Co}^{\ominus }=-0.28V$
• B. $C{d}^{2+}\left(aq\right)+Fe\left(s\right)\to Cd\left(s\right)+F{e}^{2+}\left(aq\right)$
  $E_{C{d}^{2+}/Cd}^{\ominus }=0.4V$
• C. $Cd\left(s\right)+C{o}^{2+}\left(aq\right)\to C{d}^{2+}\left(aq\right)+Co\left(s\right)$
  $E_{F{e}^{2+}/Fe}^{\ominus }=-0.44V$
• D. $Z{n}^{2+}\left(aq\right)+H_2\to Zn\left(s\right)+2H^{\oplus }$
  $E_{Z{n}^{2+}/Zn}^{\ominus }=-0.76V$

Answer 1

Answer: (B), (C)

The correct options are
B $C{d}^{2+}\left(aq\right)+Fe\left(s\right)\to Cd\left(s\right)+F{e}^{2+}\left(aq\right)$
$E_{C{d}^{2+}/Cd}^{\ominus }=0.4V$
C $Cd\left(s\right)+C{o}^{2+}\left(aq\right)\to C{d}^{2+}\left(aq\right)+Co\left(s\right)$

$E_{F{e}^{2+}/Fe}^{\ominus }=-0.44V$

Using : $E_{cell}^{\ominus }=(E_{reduction}^{\ominus }{)}_{cathode}-,(E_{reduction}^{\ominus }{)}_{anode}$

a. $E_{cell}^{\ominus }=-0.44-(-0.28)=-0.16V$

b. $E_{cell}^{\ominus }=-0.4-(-0.44)=+0.04V$

c. $E_{cell}^{\ominus }=-0.28-(-0.4)=0.12V$

d. $E_{cell}^{\ominus }=(-0.76)-0=-0.76V$

The reaction for which $E_{cell}^{\ominus }$ is positive , the $\Delta G<0$.

Hence, that reaction will be spontaneous.

So, option B and C are correct.