Chemistry is the section where NEET candidates can gain the most in the least time, provided the three branches are revised as three separate habits. This set covers physical chemistry calculations, organic reactions and mechanisms, and inorganic chemistry including periodic properties, chemical bonding and coordination compounds. Organic questions show the mechanism step by step so the logic carries over to unfamiliar reactions.
For a spontaneous process at constant temperature and pressure:
Answer: C
For spontaneous process: ΔG < 0. Generally also ΔS > 0 for most spontaneous processes. (ΔH < 0 is not always required)
Q.65Hard
The decomposition of H₂O₂ follows first-order kinetics with k = 0.01 s⁻¹. If initial concentration is 0.1 M, what will be the concentration after 100 seconds?
Answer: A
For first-order: [A] = [A₀]e^(-kt) = 0.1 × e^(-0.01×100) = 0.1 × e^(-1) = 0.1 × 0.368 = 0.0368 M
Q.66Hard
For the reaction: 2A + B ⇌ C, Kc = 0.5 at 298 K. If initial concentrations are [A] = 1 M, [B] = 1 M, [C] = 0, what is the equilibrium concentration of C?
Answer: A
ICE table: At equilibrium, [A] = 1-2x, [B] = 1-x, [C] = x. Kc = x/[(1-2x)²(1-x)] = 0.5. Solving: x ≈ 0.414 M
Q.67Hard
The standard electrode potentials are: Cu²⁺ + 2e⁻ → Cu, E° = 0.34 V and Ag⁺ + e⁻ → Ag, E° = 0.80 V. Which is the strongest oxidizing agent?
Answer: C
Higher the reduction potential, stronger the oxidizing agent. Ag⁺ (E° = 0.80 V) > Cu²⁺ (E° = 0.34 V). Ag⁺ is strongest oxidizer.
Q.68Hard
For a weak acid HA with Ka = 1.8 × 10⁻⁵, if 0.1 M solution is prepared, what percentage ionization occurs?
An endothermic reaction has ΔH = +50 kJ/mol. For this reaction to be spontaneous at all temperatures, which condition must be satisfied?
Answer: A
For an endothermic reaction (ΔH > 0) to be spontaneous, ΔG = ΔH - TΔS must be negative. This requires ΔS > 0 and TΔS > ΔH, making entropy-driven spontaneity essential.
Q.70Medium
The rate constant for a reaction doubles when temperature increases from 300 K to 310 K. What is the approximate activation energy (Ea)?
Which of the following factors does NOT affect the position of chemical equilibrium?
Answer: C
A catalyst speeds up both forward and reverse reactions equally, so it does not change the position of equilibrium. It only helps the system reach equilibrium faster.
Q.72Medium
For the reaction: N₂O₄(g) ⇌ 2NO₂(g), if Kp = 0.5 atm at 298 K, what is Kc at the same temperature?
Answer: D
Relationship: Kp = Kc(RT)^Δn, where Δn = 2 - 1 = 1. Therefore, Kc = Kp/(RT) = 0.5/(RT). But using proper units, Kc = 0.5/(RT)² when pressure is in atm and volume in L.
Q.73Easy
A solution has [H⁺] = 10⁻⁴ M at 25°C. What is the pH and pOH of this solution?
What is the order of the reaction if its half-life is independent of initial concentration?
Answer: B
For first-order reactions, t₁/₂ = 0.693/k, which is independent of initial concentration. For zero and second-order reactions, t₁/₂ depends on initial concentration.
Q.75Easy
In a galvanic cell, which statement is always true?
Answer: D
In a galvanic cell, the anode is where oxidation occurs and is the negative electrode. Electrons flow from anode to cathode through the external circuit.
Q.76Medium
The cell potential (E°cell) for a reaction is -0.5 V. Which statement is correct?
Answer: B
When E°cell is negative, ΔG° = -nFE°cell is positive, making the reaction non-spontaneous. Also, negative E°cell indicates Kequilibrium < 1.
Q.77Hard
If ΔG° = -40 kJ/mol at 298 K, what is the order of magnitude of the equilibrium constant K?
Answer: C
ΔG° = -RT ln K. With ΔG° = -40 kJ/mol = -40000 J/mol, ln K = 40000/(8.314 × 298) ≈ 16.2, so K = e^16.2 >> 1 (very large).
Q.78Easy
Which colligative property is independent of the nature of the solute?
Answer: D
All colligative properties (boiling point elevation, freezing point depression, osmotic pressure, and vapor pressure lowering) depend only on the number of solute particles, not their nature.
Q.79Medium
A solution containing 0.5 mol of a non-volatile, non-electrolyte solute in 1 L of water shows a freezing point of -0.93°C. What is the cryoscopic constant (Kf) of water? (Tf of pure water = 0°C)
Answer: B
ΔTf = Kf × m, where m = molality = 0.5 mol/1 kg (approximately). ΔTf = 0.93°C, so Kf = 0.093.5 = 1.86 K·kg/mol.
Q.80Medium
The osmotic pressure of a solution is 10 atm at 27°C. What is the molarity of the solution?
Answer: A
π = MRT, where π = 10 atm, T = 300 K, R = 0.0821 L·atm/(mol·K). M = π/(RT) = 10/(0.0821 × 300) ≈ 0.41 M.
