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
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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.
