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02Class 12 Chemistry

Electrochemistry formulas

Cell potential, Nernst equation, conductance and electrolysis formulas for Electrochemistry. Questions are usually direct once you've identified the half-reactions.

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All Chemistry formulas

Cells

Cell potential
Ecell∘=Ecathode∘−Eanode∘\displaystyle E^\circ_{\text{cell}} = E^\circ_{\text{cathode}} - E^\circ_{\text{anode}}
Nernst equation
E=E∘−0.0591nlog⁡Q\displaystyle E = E^\circ - \frac{0.0591}{n}\log Q

At 298 K.

Gibbs energy
ΔG∘=−nFE∘\displaystyle \Delta G^\circ = -nFE^\circ
Equilibrium constant
log⁡K=nE∘0.0591\displaystyle \log K = \frac{nE^\circ}{0.0591}

At 298 K.

Conductance

Resistance
R=ρlA\displaystyle R = \rho\frac{l}{A}
Conductivity
κ=1ρ=G∗R\displaystyle \kappa = \frac{1}{\rho} = \frac{G^*}{R}

G* is the cell constant, l/A.

Molar conductivity
Λm=κ×1000C\displaystyle \Lambda_m = \frac{\kappa\times1000}{C}

κ in S cm⁻¹ and C in mol L⁻¹.

Kohlrausch's law
Λm∘=ν+λ+∘+ν−λ−∘\displaystyle \Lambda_m^\circ = \nu_+\lambda_+^\circ + \nu_-\lambda_-^\circ
Strong electrolytes
Λm=Λm∘−AC\displaystyle \Lambda_m = \Lambda_m^\circ - A\sqrt{C}
Degree of dissociation
α=ΛmΛm∘\displaystyle \alpha = \frac{\Lambda_m}{\Lambda_m^\circ}

Electrolysis

Faraday's first law
m=ZIt=EItF\displaystyle m = ZIt = \frac{EIt}{F}

E is the equivalent weight, and F = 96500 C/mol.

Faraday's second law
m1m2=E1E2\displaystyle \frac{m_1}{m_2} = \frac{E_1}{E_2}

Where students slip up

  • Multiplying E° by the balancing coefficients. It's an intensive property, so it doesn't change.
  • Reversing Q in the Nernst equation. It's products over reactants.
  • Thinking molar conductivity falls with dilution. Conductivity falls, while molar conductivity rises.

Try it on your weakest chapter.

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