COMEDK UGET Chemistry - Physical Chemistry Syllabus

Define enthalpy (H) and the relation between ΔH and ΔU.

H = U + PV; ΔH = ΔU + Δ(PV), and for gases ΔH = ΔU + Δn_g RT at constant T.

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 (ΔH is path-independent, a state function).

State the second law of thermodynamics in terms of entropy.

The entropy of an isolated system always increases for a spontaneous process; ΔS_universe > 0.

Give the Gibbs free energy equation and the spontaneity criterion.

ΔG = ΔH − TΔS; the process is spontaneous when ΔG < 0, at equilibrium when ΔG = 0, non-spontaneous when ΔG > 0.

What is the relation between standard Gibbs free energy and the equilibrium constant?

ΔG° = −RT ln K.

Differentiate between extensive and intensive properties with examples.

Extensive depend on amount of matter (mass, volume, enthalpy); intensive do not (temperature, pressure, density, molarity).

State Le Chatelier's principle.

When a system at equilibrium is disturbed by a change in concentration, pressure, or temperature, it shifts to counteract the change and restore equilibrium.

Write Kc and Kp for the reaction and the relation between them.

Kc uses molar concentrations, Kp uses partial pressures; Kp = Kc(RT)^Δn_g, where Δn_g = moles gaseous products − reactants.

How does an increase in pressure affect a gaseous equilibrium?

Increasing pressure shifts the equilibrium toward the side with fewer moles of gas; no shift if moles of gas are equal on both sides.

Define the reaction quotient Q and its use.

Q has the same form as K but uses current concentrations. If Q < K reaction goes forward, Q > K reverse, Q = K at equilibrium.

State the Arrhenius and Brønsted-Lowry definitions of acids and bases.

Arrhenius: acid gives H⁺, base gives OH⁻ in water. Brønsted-Lowry: acid is a proton donor, base is a proton acceptor.

Give the Lewis definition of acids and bases.

A Lewis acid accepts an electron pair; a Lewis base donates an electron pair.

What is the ionic product of water (Kw) at 25 °C?

Kw = [H⁺][OH⁻] = 1.0 × 10⁻¹⁴ at 25 °C.

Define pH and pOH and their relationship.

pH = −log[H⁺], pOH = −log[OH⁻]; pH + pOH = 14 at 25 °C.

What is a buffer solution and the Henderson-Hasselbalch equation?

A buffer resists pH change on adding small amounts of acid/base. pH = pKa + log([salt]/[acid]).

Define solubility product (Ksp) and the common ion effect.

Ksp is the equilibrium constant for dissolution of a sparingly soluble salt. Common ion effect: solubility decreases when a common ion is added, suppressing dissociation.

State Raoult's law for a solution of two volatile liquids.

The partial vapour pressure of each component equals its mole fraction times its pure vapour pressure: P_total = x_A P°_A + x_B P°_B.

What are colligative properties? Name them.

Properties depending on the number of solute particles, not their identity: relative lowering of vapour pressure, elevation of boiling point, depression of freezing point, and osmotic pressure.

Give the formula for osmotic pressure.

π = CRT = (n/V)RT, where C is molar concentration (with van't Hoff factor i: π = iCRT).

What is the van't Hoff factor (i)?

i = observed colligative property / calculated value; it accounts for dissociation (i > 1) or association (i < 1) of solute.

State Henry's law.

The solubility (mass) of a gas in a liquid is directly proportional to the partial pressure of the gas: p = K_H · x.

Define oxidation and reduction in terms of electron transfer.

Oxidation is loss of electrons (increase in oxidation number); reduction is gain of electrons (decrease in oxidation number).

What is a redox reaction and the role of oxidizing/reducing agents?

A reaction involving simultaneous oxidation and reduction. The oxidizing agent gets reduced; the reducing agent gets oxidized.

Write the Nernst equation for an electrode at 298 K.

E = E° − (0.0591/n) log Q, where n is the number of electrons transferred.

State Faraday's first law of electrolysis.

The mass of substance deposited/liberated at an electrode is directly proportional to the quantity of electricity passed (m ∝ Q); 1 mole of electrons = 1 Faraday = 96500 C.

Define molar conductivity and state Kohlrausch's law.

Molar conductivity Λm = κ × 1000 / C. Kohlrausch's law: limiting molar conductivity is the sum of independent contributions of cation and anion (Λ°m = ν₊λ°₊ + ν₋λ°₋).

How are EMF of a cell and the spontaneity related to ΔG?

ΔG = −nFE_cell; a positive E_cell (and negative ΔG) means a spontaneous cell reaction.

Define order and molecularity of a reaction.

Order is the sum of powers of concentration terms in the experimental rate law (can be fractional/zero); molecularity is the number of reacting species in an elementary step (always a whole number).

Give the integrated rate law and half-life of a first-order reaction.

k = (2.303/t) log([A]₀/[A]); t₁/₂ = 0.693/k (independent of initial concentration).

State the Arrhenius equation for the rate constant.

k = A·e^(−Ea/RT), where A is the frequency factor and Ea is the activation energy.

Distinguish physisorption from chemisorption.

Physisorption: weak van der Waals forces, low heat of adsorption (20–40 kJ/mol), reversible, multilayer, favored at low temperature. Chemisorption: chemical bonds, high heat (80–240 kJ/mol), irreversible, monolayer, increases then decreases with temperature.