Overview of Electrochemistry

An electrochemical cell that converts chemical energy of a spontaneous redox reaction into electrical energy is called a galvanic cell.

The potential difference developed between an electrode and its electrolyte is called electrode potential.

The electrode potential measured under standard conditions (1 M, 1 bar, 298 K) is called standard electrode potential.

The reference electrode assigned zero potential at all temperatures is called the standard hydrogen electrode.

The equation which relates electrode potential with concentration of ions is called the Nernst equation.

The ratio of product concentration to reactant concentration at equilibrium is called equilibrium constant.

The thermodynamic quantity representing maximum obtainable work from a reaction is called Gibbs free energy.

The resistance of a conductor of unit length and unit cross-sectional area is called resistivity.

The reciprocal of resistance is called conductance.

The conductance of a solution of unit length and unit cross-section is called conductivity.

The ratio of distance between electrodes to area of cross-section is called cell constant.

Electrode potential varies with concentration and temperature.

\[E=E^\circ-\frac{RT}{nF}\ln Q\]

At 298 K:

\[E=E^\circ-\frac{0.059}{n}\log Q\]

\[E_{cell}=E_{cathode}-E_{anode}\]

\[E_{cell}^\circ=E_{cathode}^\circ-E_{anode}^\circ\]

For reaction:

aA + bB → cC + dD

\[E_{cell}=E_{cell}^\circ-\frac{RT}{nF}\ln\frac{[C]^c[D]^d}{[A]^a[B]^b}\]

\[R=\rho\frac{l}{A}\]

\[G=\frac{1}{R}\]

\[\kappa=\frac{1}{\rho}\]

\[\kappa=\frac{G^*}{R}\]

\[G^*=\frac{l}{A}\]

\[R_2=\frac{R_1R_4}{R_3}\]

An electrochemical cell in which electrical energy is used to bring about a non-spontaneous chemical reaction is called an electrolytic cell.

A cell in which the chemical reaction occurs only once and cannot be reversed is called a primary cell.

A cell in which the chemical reaction can be reversed by passing current in opposite direction is called a secondary cell.

A galvanic cell designed to convert the energy of combustion of fuels directly into electrical energy is called a fuel cell.

\[\Lambda_m=\frac{\kappa}{C}\]

\[\Lambda_m=\kappa\times\frac{1000}{M}\]

Unit relation:

\[1Sm^2mol^{-1}=10^4Scm^2mol^{-1}\]

\[\Lambda_m=\Lambda_m^\circ-A\sqrt{C}\]

\[\alpha=\frac{\Lambda_m}{\Lambda_m^\circ}\]

Faraday’s First Law of Electrolysis states that the mass of a substance deposited or liberated at an electrode during electrolysis is directly proportional to the quantity of electricity passed through the electrolyte.

Mathematically,

m ∝ Q

m = ZQ

where m is mass deposited, Q is charge passed, and Z is electrochemical equivalent.

Faraday’s Second Law of Electrolysis states that when the same quantity of electricity is passed through different electrolytes, the masses of substances deposited are proportional to their chemical equivalent weights.

Mathematically,

\[\frac{m_1}{m_2}=\frac{E_1}{E_2}\]

where m is mass deposited and E is equivalent weight.

Kohlrausch’s Law states that at infinite dilution, each ion contributes independently to the total molar conductivity of an electrolyte, and the limiting molar conductivity is equal to the sum of individual ionic conductivities.

Mathematically,

\[\Lambda_m^\circ=\nu_+\lambda_+^\circ+\nu_-\lambda_-^\circ\]

where λ^∘₊ and λ^∘₋​ are limiting molar conductivities of cation and anion respectively.