IIT JAM CY: Physical Chemistry

Physical chemistry in IIT JAM CY is the quantitative core: quantum chemistry, thermodynamics, chemical kinetics, electrochemistry, surface chemistry, and molecular spectroscopy. Questions often ask you to set up a calculation, track units, and interpret a physical model rather than recall a name.

Core rules to have automatic

• First law (IUPAC): ΔU = q + w, with w = −P_ext ΔV for pressure–volume work; work done on the system is positive.
• Gibbs energy: ΔG° = ΔH° − TΔS°. At constant T and P, ΔG < 0 predicts spontaneity; ΔG° = −RT ln K.
• Kinetics: zero order [A] = [A]0 − kt; first order ln[A] = ln[A]0 − kt and t1/2 = ln2/k; second order 1/[A] = 1/[A]0 + kt. Arrhenius: k = A exp(−Ea/RT).
• Particle in a 1D box: E_n = n²h²/(8mL²), n = 1, 2, 3, …; energy gaps shrink as L grows.
• Spectroscopy: rotational spacings are ~2B; vibrational harmonic frequency depends on √(k/μ); electronic transitions obey ΔS = 0 for spin-allowed bands.

Worked example

For a first-order reaction with k = 3.47 × 10^−3 s^−1, find t1/2 and the fraction left at 500 s. t1/2 = ln2/k = 0.693/(3.47 × 10^−3 s^−1) = 2.00 × 10^2 s. Fraction remaining = [A]/[A]0 = exp(−kt) = exp[−(3.47 × 10^−3)(500)] = exp(−1.735) = 0.176. About 17.6% remains. The reasoning is to use the integrated first-order law, not the half-life alone.

Traps

Mixing °C with K in ΔG; forgetting that Δn_gas changes ΔH vs ΔU; using k in min^−1 with t in seconds; treating n = 0 as allowed in the box; ignoring reduced mass in vibrational frequency; and reporting ΔG° as spontaneity at nonstandard conditions.