Students can go through TS Inter 2nd Year Chemistry Notes 3rd Lesson Electrochemistry and Chemical Kinetics will help students in revising the entire concepts quickly.
TS Inter 2nd Year Chemistry Notes 3rd Lesson Electrochemistry and Chemical Kinetics
→ In an electrolytic cell electrical energy is converted into chemical energy while in Galvanic cell or Voltaic cell chemical energy is converted into electrical energy.
→ In both galvanic and electrolytic cells oxidation take place at anode and reduction take place at cathode.
→ Nernst equation gives the dependence of the electrode. Potential on the concentration of ions with which the electrode is reversible.
→ For a metal electrode the reduction reaction is Mnn+ + ne– ⇌ M. The Nernst equation to calculate the electrode potential at different concentration is
E = E° – \(\frac{2.303 \mathrm{RT}}{\mathrm{nF}}\) log \(\frac{[\mathrm{M}]}{\left[\mathrm{M}^{\mathrm{n}+}\right]}\)
E = E° – \(\frac{2.303 \mathrm{RT}}{\mathrm{nF}}\)log C
Since M is solid, its activity will be unity.
→ For a non – metal electrode the reduction reaction is A + ne– ⇌ An-. The Nernst equation to calculate electrode potential at different concentration is
E = E° – \(\frac{2.303 \mathrm{RT}}{\mathrm{nF}}\) log\(\frac{\left[\mathrm{A}^{\mathrm{n}-}\right]}{\left[\mathrm{A}^{-}\right]}\) or
E = E – \(\frac{2.303 \mathrm{RT}}{\mathrm{nF}}\) log [An-]
→ General equation for electrode potential of any electrode is
E = E° – \(\frac{2.303 \mathrm{RT}}{\mathrm{nF}}\) log\(\frac{\text { [Products }]}{[\text { Reactan } t s]}\)
→ For a cell reaction of the type aA + bB ⇌ cC + dD
The Nernst equation
E = E° – \(\frac{0.0591}{n}\) log \(\frac{[\mathrm{C}]^{\mathrm{c}}[\mathrm{D}]^{\mathrm{d}}}{[\mathrm{A}]^{\mathrm{a}}[\mathrm{B}]^{\mathrm{b}}}\)
→ From the standard Gibbs energy the equilibrium constant by the equation
ΔG° = – RT /n K.
→ Substances whose melts or aqueous solutions conduct electric current are called electrolytes. All salts, acids and based are referred to as electrolytes.
→ Substances whose melts or aqueous solutions do not conduct are called non – electrolytes e.g. non – polar covalent substances like urea, glucose, sugar etc., are non – electrolyte.
→ The flow of electrons across the boundary is accompanied by chemical reaction i.e., oxidation-reduction. Such a reaction is called electrolysis. Electrolysis take place only at electrodes.
→ If a substance ionise completely, it is known as strong electrolyte while the substances which show very little ionisation in solution are called weak electrolytes.
→ Kohlrausch’s law states that the equivalent conductivity of an electrolyte at infinite dilution (λ0) is the sum of the equivalent conductivities of the cation and anions.
λ0 = λ0+ + λ0–
where λ0+ is the ionic conductance of
the cation and λ0– is the ionic conductance of the anion.
→ Kohlrauch law is also useful to calculate As for any electrolyte from the X° of individual ions.
→ Equivalent conductance of weak electrolytes can be calculated from the conductances of completely dissociated strong electrolytes
e.g. Λ°CH3COOH = Λ°CH3COONa + Λ°HCl – Λ°NaCl
→ First law : The amount of the substance liberated or deposited or dissolved at an electrode during electrolysis of an electro¬lyte is directly proportional to the quantity of electricity passing through the solution of electrolyte or the melt.
→ Electrochemical equivalent of a substance is the amount of substance deposited or liberated or dissolved or underwent electrode reaction at an electrode by passing one ampere current for one second i.e., one coulomb.
→ One Faraday i.e., 96,500 coloumbs is equal to the charge present on one mole
(6.023 × 1023) of electrons or protons.
m = \(\frac{E \times c \times t}{96500}\)
∴ e = \(\frac{E}{96500}\)
→ Second law of Faraday states that, if the same quantity of electricity is passed through different electrolyte solutions or melts the amount of the different substances liberated or deposited or dissolved or had undergone reaction at the electrode are directly pro¬portional to their chemical equivalents.
\(\frac{W_1}{E_1}=\frac{W_2}{E_2}=\frac{W_3}{E_3}\)
→ A primary cell is a cell in which the electrical energy is obtained at the expense of chemical reactions. A primary cell works as long as the active chemicals reacting. The dry cell which generates a voltage of ~ 1.25 – 1.50V is an example of the primary cell.
→ A secondary cell is a cell in which the electrode reactions are reversed by the appli¬cation of an external current. Hence such a cell once used can be recharged.
→ Corrosion is a process of deterioration and consequent loss of solid metallic material through an unwanted chemical or electro-chemical attack by its environment, starting at the surface.
→ Corrosion is prevented by coating the metal surface with a thin film of paint, grease, metal (eg : Zn, Sn, Ni, Cu, Cr), metal oxide (eg: Fe3O4).
→ The rate of reaction is defined as the change in molar concentration of reactant or product per unit time.
→ At anytime the rate of reaction depends on the concentration of the reactants at that instant.
→ The units of rate of reaction are moles litre-1 sec-1 or moles litre-1 min-1 or moles litre-1 hr-1.
→ The rate of reaction is directly proportional to the (concentration of the reactants)11 or Cn.
→ For gaseous reactions the rate of reaction is directly proportional to (pressure of the reactants)”.
→ Generally rise of 10°C in temperature doubles the specific rate of reaction.
→ Catalyst increases the rate of reaction by changing the path of the reaction i.e., mak-ing the reaction to proceed in the path pf lower activation energy.
→ The mathematical expression of the rate of reaction on concentration terms of reac¬tants is known as rate expression or rate equation or rate law.
→ Units of rate constant are mole1-n litren-1 sec-1.
→ The total number of reactant molecules tak-ing part in the slowest step or rate limiting step or in the formation of intermediate species is known as molecularity of the reaction.
→ The order of a reaction is the total number of molecules whose concentrations changes during the chemical reaction or the sum of the powers of the concentration terms in the rate equation.
→ Reactions in which the rate of reaction is independent of the concentration of the reacting substances is called zero order reactions.
→ The reactions which appear to be higher order actually follow lower order Kinetics are called Pseudo Chemical reactions e.g. acid catalysed ester hydrolysis and hydrolysis of cane sugar to give glucose are pseudo first order reactions.
→ The reactions in which the products formed in the first stage may react with each other or with the original reactant to give new products are known as consecutive reactions.
→ The reactions proceeding in a series of successive reactions initiated by a suitable primary process are called chain reactions.
e.g. Formation of HCl from H2 and Cl2 and Chlorination of alkanes.
→ The minimum energy which must be associated with reactant molecules so that their mutual collision result in a chemical reaction is called Threshold energy.
→ Collisions which yield the product are called effective collisions or fruitful collisions or activated collisions.
→ The difference in energy between the threshold energy and the energy of the normal colliding molecules is known as activation energy.
Activation energy = Threshold energy – Energy of normal colliding molecules
→ The ratio of the rate constants at two different temperatures (preferably 35°C and 25°C) is known as temperature coefficient.