CSIR NET Chemical Sciences Physical Chemistry Syllabus

State the first law of thermodynamics and its equation.

Energy can be neither created nor destroyed (conservation of energy). ΔU = q + w, where ΔU is change in internal energy, q is heat added to the system, and w is work done on the system (IUPAC sign convention).

How are ΔH and ΔU related for a reaction involving gases?

ΔH = ΔU + Δ(PV) = ΔU + Δnₘ RT, where Δnₘ is the change in moles of gas (products − reactants). At constant pressure ΔH = q_p; at constant volume ΔU = q_v.

State Hess's law of constant heat summation.

The total enthalpy change of a reaction is the same whether it occurs in one step or several steps, because enthalpy is a state function. Enthalpies of individual steps can be added to get the overall ΔH.

State the second law of thermodynamics in terms of entropy.

The entropy of an isolated system (the universe) always increases for a spontaneous process: ΔS_universe = ΔS_system + ΔS_surroundings > 0. For a reversible process, ΔS_universe = 0.

Define entropy change for a reversible process and give its units.

dS = δq_rev/T, so ΔS = ∫δq_rev/T. Entropy is a state function measuring disorder/dispersal of energy. Units: J K⁻¹ mol⁻¹.

State the third law of thermodynamics.

The entropy of a perfect, pure crystalline substance is zero at absolute zero temperature (0 K). This provides an absolute reference allowing calculation of absolute entropies (standard molar entropies).

Why can absolute zero never be reached, according to thermodynamics?

It is impossible to reduce the temperature of any system to 0 K in a finite number of steps (the unattainability statement, a consequence of the third law), because removing the last bit of thermal energy/entropy requires infinite steps.

Define Gibbs free energy and give the spontaneity criterion at constant T and P.

G = H − TS, so ΔG = ΔH − TΔS. At constant T and P: ΔG < 0 spontaneous, ΔG = 0 equilibrium, ΔG > 0 non-spontaneous.

What is the relationship between ΔG° and the equilibrium constant K?

ΔG° = −RT ln K. A negative ΔG° (K > 1) favors products; positive ΔG° (K < 1) favors reactants. Also, under non-standard conditions ΔG = ΔG° + RT ln Q.

Define Helmholtz free energy and its spontaneity criterion.

A = U − TS, so ΔA = ΔU − TΔS. At constant temperature and volume, ΔA < 0 indicates a spontaneous process; ΔA equals the maximum work obtainable (other than expansion work is included as total work).

State Kohlrausch's law of independent migration of ions.

At infinite dilution, the molar conductivity of an electrolyte is the sum of the independent contributions of its cation and anion: Λ°ₘ = ν₊λ°₊ + ν₋λ°₋. It allows calculation of Λ°ₘ for weak electrolytes.

How does molar conductivity vary with dilution for strong vs weak electrolytes?

Strong electrolytes: Λₘ increases slightly with dilution and follows Λₘ = Λ°ₘ − b√c (Debye–Hückel–Onsager). Weak electrolytes: Λₘ increases sharply near infinite dilution due to increased degree of dissociation.

What is cell constant and how is conductivity (κ) related to conductance (G)?

Cell constant = l/A (distance between electrodes / area). Conductivity κ = G × (l/A) = (1/R) × cell constant. Molar conductivity Λₘ = κ × 1000/c (with c in mol/L).

What is the difference between a galvanic cell and an electrolytic cell?

Galvanic (voltaic) cell: spontaneous redox reaction produces electrical energy (ΔG < 0); anode is negative, cathode positive. Electrolytic cell: electrical energy drives a non-spontaneous reaction; anode is positive, cathode negative.

In a galvanic cell, what reactions occur at the anode and cathode?

Oxidation occurs at the anode (electrons released), reduction occurs at the cathode (electrons consumed). Mnemonic: 'An Ox, Red Cat'. Electrons flow from anode to cathode through the external circuit.

Write the Nernst equation for an electrode/cell at 298 K.

E = E° − (RT/nF) ln Q = E° − (0.0591/n) log Q at 298 K, where n = electrons transferred, F = Faraday constant, Q = reaction quotient. It relates electrode/cell potential to concentrations.

What is the standard hydrogen electrode (SHE) and its assigned potential?

The SHE is the reference electrode: Pt | H₂(1 atm) | H⁺(1 M), assigned a standard electrode potential of exactly 0.00 V at all temperatures. All other electrode potentials are measured relative to it.

How is the standard cell EMF related to standard electrode potentials, and to ΔG°?

E°cell = E°cathode − E°anode (both as reduction potentials). ΔG° = −nFE°cell; a positive E°cell corresponds to a spontaneous reaction (negative ΔG°).

Give two applications of electrochemical cells / potential measurements.

Examples: determining pH using a glass/calomel electrode; measuring solubility products (Ksp) and equilibrium constants via E°; potentiometric titrations; corrosion studies; and powering devices (batteries, fuel cells).

For the equilibrium of a reaction, how are Kp and Kc related?

Kp = Kc(RT)^Δnₘ, where Δnₘ = (moles of gaseous products − moles of gaseous reactants). When Δnₘ = 0, Kp = Kc.

State Le Chatelier's principle.

When a system at equilibrium is subjected to a change in concentration, temperature, or pressure, the equilibrium shifts in the direction that counteracts (partially offsets) the imposed change.

According to Le Chatelier's principle, how does increasing pressure affect a gaseous equilibrium?

Increasing pressure (decreasing volume) shifts equilibrium toward the side with fewer moles of gas. If moles of gas are equal on both sides, pressure has no effect on the position of equilibrium.

Define the common ion effect and its consequence on solubility.

The common ion effect is the suppression of ionization of a weak electrolyte (or decrease in solubility of a sparingly soluble salt) by adding an ion already present in the equilibrium. It shifts equilibrium per Le Chatelier, lowering dissociation/solubility.

State the Henderson–Hasselbalch equation for a buffer.

pH = pKa + log([conjugate base]/[acid]) (for an acidic buffer). For a basic buffer: pOH = pKb + log([conjugate acid]/[base]). It relates buffer pH to the ratio of components.

What is the difference between physisorption and chemisorption?

Physisorption: weak van der Waals forces, low enthalpy (20–40 kJ/mol), reversible, multilayer, decreases with rising temperature, not specific. Chemisorption: chemical bonds, high enthalpy (80–240 kJ/mol), often irreversible, monolayer, specific, may increase then decrease with temperature.

State the Freundlich and Langmuir adsorption isotherm key features.

Freundlich: x/m = k·P^(1/n) (empirical, no saturation, multilayer at high pressure). Langmuir: x/m = (a·P)/(1 + b·P), assumes monolayer adsorption on uniform sites with no interaction; gives saturation at high pressure.

What is the difference between a lyophilic and lyophobic colloid?

Lyophilic (solvent-loving): reversible, stable, self-forming, high solvent affinity (e.g., starch, gelatin). Lyophobic (solvent-hating): irreversible, less stable, need stabilizers, prepared by special methods (e.g., metal/As₂S₃ sols).

What is the Tyndall effect and what does it indicate?

The scattering of a beam of light by colloidal particles, making the light path visible. It distinguishes colloidal solutions (show Tyndall effect) from true solutions (do not), because colloidal particle size is comparable to/larger than light wavelength.

Define surface tension and state how it changes with temperature.

Surface tension is the force per unit length acting along the surface of a liquid (units N/m), arising from unbalanced cohesive forces at the surface (minimizes surface area). It decreases with increasing temperature and becomes zero at the critical temperature.

What is the difference between homogeneous and heterogeneous catalysis (catalysis by surfaces)?

Homogeneous: catalyst and reactants in the same phase. Heterogeneous (surface) catalysis: catalyst in a different phase (usually solid catalyst with gas/liquid reactants); reaction occurs on the surface via adsorption, reaction, and desorption of products.

What are the seven crystal systems and how many Bravais lattices exist?

Seven crystal systems: cubic, tetragonal, orthorhombic, monoclinic, triclinic, hexagonal, and rhombohedral (trigonal). There are 14 Bravais lattices in total.

Compare the packing efficiency and coordination number of SCC, BCC, and FCC.

Simple cubic: CN 6, packing 52.4%, 1 atom/cell. Body-centered cubic: CN 8, packing 68%, 2 atoms/cell. Face-centered cubic (CCP): CN 12, packing 74%, 4 atoms/cell (most efficient).

State Bragg's law of X-ray diffraction.

nλ = 2d sinθ, where n = order of diffraction, λ = X-ray wavelength, d = interplanar spacing, and θ = glancing/Bragg angle. It gives the condition for constructive interference of X-rays from crystal planes.

What is the difference between Schottky and Frenkel defects?

Schottky defect: equal numbers of cation and anion vacancies (decreases density); favored when ions are similar in size (e.g., NaCl). Frenkel defect: a cation displaced to an interstitial site (density unchanged); favored when cation is much smaller than anion (e.g., AgCl, ZnS).

How do n-type and p-type semiconductors arise from doping?

n-type: doping with a higher-valence (electron-rich) impurity (e.g., Si doped with P) adds free electrons as charge carriers. p-type: doping with a lower-valence (electron-deficient) impurity (e.g., Si doped with B) creates positive 'holes' as carriers.

Distinguish addition (chain-growth) and condensation (step-growth) polymerization.

Addition: monomers with C=C add without losing any atoms, via chain mechanism (initiation, propagation, termination); e.g., polyethylene. Condensation: monomers with two functional groups join with elimination of a small molecule (e.g., H₂O); e.g., nylon, polyester.

Define number-average (M̄n) and weight-average (M̄w) molecular weights, and the polydispersity index (PDI).

M̄n = ΣNᵢMᵢ/ΣNᵢ (counts molecules). M̄w = ΣNᵢMᵢ²/ΣNᵢMᵢ (weights by mass; ≥ M̄n). PDI = M̄w/M̄n ≥ 1; PDI = 1 means a monodisperse polymer.

What are biodegradable polymers? Give two examples.

Polymers that can be broken down by microorganisms/enzymes into simpler harmless products (CO₂, H₂O, biomass). Examples: PHBV (poly-β-hydroxybutyrate-co-β-hydroxyvalerate), PLA (polylactic acid), Nylon-2-nylon-6, and PGA (polyglycolic acid).