Ncert Exercises & Solutions

3.6 In the button cells widely used in watches and other devices the following reaction takes place:

Zn(s) + Ag₂O(s) + H₂O(l) → Zn²⁺(aq) + 2Ag(s) + 2OH^–(aq)

Determine ∆r GƟ and EƟ for the reaction.

Step 1:

The reaction is as follows:

Zn(s) + Ag₂O(s) + H₂O(l) → Zn²⁺(aq) + 2Ag(s) + 2OH^–(aq)

Here, n =2

Calculate the value of E^o cell as follows:

\(E_{Zn/Zn^{+2}}^{o} = 0.76 V \\ E_{Ag^{+}/Ag}^{o}= 0.80 V \)

\(E_{cell}^{o}=E_{Zn/Zn^{2+}}^{o}+E_{Ag^{+}/Ag}^{o}\)
\(E_{cell}^{o}=0.76+0.80\)
\(E_{cell}^{o}\)= 1.56 V

Step 2:

Calculate the value of \(\Delta_{r} G^{o}\) is as follows:
\(\Delta_{r} G^{o} =-nFE_{cell} ^{o}\)
\(= -2\times 96487\times 1.56\)
=-301,039.4 J/mol
=-301.01 kJ/mol

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