Physical and Chemical Sciences
What this domain tests
Physical and Chemical Sciences covers atomic and molecular structure, thermodynamics, kinetics, equilibrium, electrochemistry, spectroscopy and nuclear chemistry. BARC uses this section to test whether you can move between a microscopic model and a measurable quantity.
Core rules
- Quantum numbers n, l, m_l and m_s, together with the Pauli exclusion principle, Aufbau principle and Hund's rules, set electron configurations.
- Bonding: VSEPR predicts geometry; hybridisation explains σ and π frameworks; molecular-orbital theory explains magnetism and bond order.
- Thermodynamics: ΔG = ΔH − TΔS; ΔG < 0 means spontaneous at constant T and P; ΔG° = −RT ln K.
- Kinetics: rate = k[A]^m[B]^n; first-order t½ = ln2/k; Arrhenius k = A exp(−Ea/RT).
- Spectroscopy: IR identifies functional groups; UV-Vis shows conjugation; ¹H NMR splitting follows the n+1 rule for equivalent neighbours, and chemical shift reports the environment.
Worked example
A first-order reaction has t½ = 20 min. Then k = ln2/t½ = 0.693/20 = 0.03465 min^-1. After 60 min, exactly three half-lives have passed, so the fraction remaining is (1/2)^3 = 1/8 = 12.5%. The reasoning uses the defining property of first-order kinetics: the half-life is independent of initial concentration.
Traps
- Confusing reaction order with molecularity.
- Using ΔG° to predict spontaneity under non-standard conditions.
- Forgetting that pH + pOH = 14 only near 25 °C.
- Counting non-equivalent neighbours in NMR splitting.
- Mixing up oxidation and reduction at electrodes.