Chemistry — Physical Chemistry for the JEE Main Exam

Common failure modes

These are the patterns that cause most candidates to lose marks on this topic. Recognising them in advance is half the work.

• !Confusing ΔG with ΔG° — forgetting the Q (reaction quotient) term in ΔG = ΔG° + RT ln Q
• !Misapplying the Nernst equation when concentrations are non-standard
• !Using first-order half-life formula for a second-order reaction
• !Forgetting to convert temperature to Kelvin in Arrhenius and thermodynamic equations
• !Misidentifying buffer problems — Henderson-Hasselbalch requires a weak acid and its conjugate base, not any two acids

Study tips

• 1Build a formula card for physical chemistry: ΔG = ΔH − TΔS, Nernst equation, Arrhenius equation, Van't Hoff factor, and Raoult's law. JEE Main is formula-driven here.
• 2Practice electrochemistry cell-notation reading — JEE routinely asks cell EMF from given half-reactions.
• 3Drill rate-law problems by order determination from experimental data (method of initial rates).
• 4For solutions, practice colligative property calculations: depression of freezing point, elevation of boiling point, osmotic pressure.
• 5Do at least 5 past-paper thermodynamics questions per sitting — the multi-step Hess's law + entropy problems are high-value.

Sample JEE Main Chemistry — Physical Chemistry questions

These sample items mirror the format and difficulty of real JEE Main questions. Practice with thousands more on the free Koydo question bank.

1. 1

   For a reaction at equilibrium at 298 K, if ΔG° = −5.7 kJ/mol, the equilibrium constant K is approximately (R = 8.314 J/mol·K):

   • A10Correct
   • B100
   • C1000
   • D0.1
   Why this answer?

   Illustrative JEE-style: ΔG° = −RT ln K, so ln K = −ΔG°/(RT) = 5700/(8.314 × 298) ≈ 2.30, giving K ≈ e^2.30 ≈ 10.

2. 2

   For a first-order reaction, the time required for 75% completion is:

   • At½
   • B2t½Correct
   • C3t½
   • D4t½
   Why this answer?

   Illustrative JEE-style: At 75% completion, 25% remains. Using N = N₀(1/2)^n, 0.25 = (1/2)^n gives n = 2. So time = 2t½.

3. 3

   Electrolysis of water produces hydrogen and oxygen in a volume ratio of:

   • A1 : 1
   • B2 : 1Correct
   • C1 : 2
   • D4 : 1
   Why this answer?

   Illustrative JEE-style: 2H₂O → 2H₂ + O₂. At the same temperature and pressure, volumes are proportional to moles, giving H₂ : O₂ = 2 : 1.