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Electrochemistry

Long Answer Type

111. What is the Nernst equation for the Potential of an electrode? Can Nernst equation be applied to the cell relation ? Apply this equation to a general reaction.
$aA + bB \to cC + dD$

The concentration of all species involved in the species involved in the electrode reaction is unity.This need not be always true.
Nernst shows that for the electrode reaction:

M^{n +} (aq) + {ne}^{-} \to M (s)

the electrode potential at any concentration measured with respect to standard hydrogen electrode can be represented by:

E_{(\frac{M^{n +}}{M})} = E_{\frac{M^{n +}}{M}}^{-} - \frac{RT}{nF} In \frac{[M]}{[M^{n +}]}

but concentration of solid M is taken as unity as we have

E_{(\frac{M^{n +}}{M})} = E_{\frac{M^{n +}}{M}}^{-} - \frac{RT}{nF} In \frac{[1]}{[M^{n +}]}

R is gas constant (8.314 JK–1 mol–1),
F is Faraday constant (96487 C mol^–1), T is temperature in kelvin and [Mⁿ⁺] is the concentration of the species, Mn

Let us take a electrode reaction

{Zn}^{2 +} + 2 e^{-} \to Zn

The Nernst equation of this electrode

E = E ° - \frac{2.303 RT}{nF} \log \frac{a_{product}}{a_{reactant}}

Instead of activity, we can take molar concentration.

E = E ° - \frac{0.05916}{n} \log \frac{[Zn]}{[{Zn}^{2 +}]}

For pure solid and liquid molar concentration is taken as unity.

E = E ° - \frac{0.05916}{2} \log \frac{1}{[{Zn}^{2 +}]}

Yes, Nernst equation can be applied to the cell reaction.

aA + bB \to cC + dD

E = E ° - \frac{0.05916}{n} \log \frac{{[C]}^{c} {[D]}^{d}}{{[A]}^{a} {[B]}^{b}}

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112. Explain Kohlrausch’s law of independent migration of ions. Mention one application of Kohlrausch’s law.

900 Views

Short Answer Type

113. How does molar conductivity vary with concentration for (i) weak electrolyte and for (ii) strong electolyte? Give reasons for these variations.

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114. State and explain Faraday's law of electrolysis?

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Long Answer Type

115. State and explain Faraday's law of electrolysis?

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116. Show that the electrical work obtainable from a galvanic cell is given by the expression.

∆ G ° = - nFE °_{cell}

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Short Answer Type

117. What are fuel cells? Write the reaction of a oxygen hydrogen fuel cell.

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118.

What is a mercury cell? Give the electrode reactions?

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119. What is the effect of change in (a) concentration, (b) temperature on the electrode potential of a given half-cell?

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120. Iron does not rust even if the zinc coating is broken in a galvanised iron pipe but, rusting occurs much faster if the tin coating over iron is broken. Explain?

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