A buffer solution is prepared by mixing 100 mL of 0.1 M acetic acid (CH₃COOH) and 100 mL of 0.1 M sodium acetate (CH₃COONa). Using Henderson-Hasselbalch equation, if Ka = 1.8 × 10⁻⁵, what is the pH?
For a reversible reaction at equilibrium, if Kc = 4 at 25°C, what is the relationship between forward and reverse rate constants?
Answer: A
At equilibrium, Kc = kf/kr. Given Kc = 4, this means kf = 4kr, indicating the forward reaction is faster than the reverse reaction.
Q.3Medium
Which of the following will shift the equilibrium of the reaction CO(g) + H₂O(g) ⇌ CO₂(g) + H₂(g), ΔH = -41 kJ/mol to the right?
Answer: A
This is an exothermic reaction (ΔH negative). By Le Chatelier's principle, decreasing temperature shifts equilibrium towards the products (right), favoring the exothermic forward reaction.
Q.4Medium
For a spontaneous process, which of the following is always true?
Answer: C
A process is spontaneous when ΔG < 0. Neither ΔH nor ΔS alone determines spontaneity; it depends on their combined effect at a given temperature.
Q.5Medium
A reaction has Ea (forward) = 50 kJ/mol and Ea (reverse) = 35 kJ/mol. What is ΔH for this reaction?
Answer: B
ΔH = Ea(forward) - Ea(reverse) = 50 - 35 = 15 kJ/mol. The positive value indicates an endothermic reaction.
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Q.6Medium
The vapour pressure of water at 25°C is 23.76 mmHg. What is the mole fraction of ethanol in an ethanol-water solution if its vapour pressure is 20.88 mmHg? (Assume ideal solution and pure ethanol vapour pressure = 58.9 mmHg at 25°C)
Answer: A
Using Raoult's law for partial pressures and ideal solutions: Total P = P₁X₁ + P₂X₂. Solving for mole fraction of ethanol: X_ethanol = (Total P - P_water)/(P_ethanol - P_water) ≈ 0.30
Q.7Medium
Which statement correctly describes the colligative properties?
Answer: B
Colligative properties (boiling point elevation, freezing point depression, osmotic pressure, vapour pressure lowering) depend only on the number of solute particles, not on their chemical nature.
Q.8Medium
A solution of HCl has pH 2. What is the degree of dissociation of HCl if initial concentration is 0.1 M?
Answer: C
If pH = 2, then [H⁺] = 10⁻² = 0.01 M. For a 0.1 M HCl solution, α = [H⁺]/C₀ = 0.001.1 = 0.1. However, HCl is a strong acid with α ≈ 1.0 (essentially complete dissociation).
Q.9Medium
A gas mixture contains 2 moles of O₂ and 3 moles of N₂. At total pressure of 5 atm, what is the partial pressure of O₂?
Which colligative property depends on the nature of solute as well as its concentration?
Answer: A
Osmotic pressure depends on solute nature because it involves membrane interactions. Other colligative properties depend only on number of solute particles
Q.11Medium
For a buffer solution containing equal molar amounts of acetic acid and sodium acetate, if Ka = 1.8 × 10⁻⁵, what is the pH?
An ideal gas undergoes isothermal compression from 10 L to 5 L at constant temperature. The work done ON the gas is:
Answer: A
In compression, volume decreases and work is done ON the gas, making w positive (in physics convention). W = -nRT ln(Vf/Vi) where Vf < Vi
Q.13Medium
The Born-Landé equation is used to calculate which property?
Answer: B
Born-Landé equation specifically calculates lattice energy of ionic compounds based on ionic radii and charges
Q.14Medium
For the reaction: PCl₅(g) ⇌ PCl₃(g) + Cl₂(g), if initial pressure of PCl₅ is 1 atm and degree of dissociation is 0.4, what is Kp at constant total pressure?
In a galvanic cell, if ΔG° = -95.5 kJ/mol and n = 2, what is E°cell? (F = 96500 C/mol)
Answer: A
ΔG° = -nFE°, so E° = -ΔG°/(nF) = 95500/(2 × 96500) = 0.495 V
Q.18Medium
The rate of reaction doubles when temperature increases from 300 K to 310 K. Calculate the activation energy (Ea) using Arrhenius equation.
Answer: A
Using ln(k₂/k₁) = (Ea/R)(T₂-T₁)/(T₁T₂), ln(2) = (Ea/8.314)(10)/(93000). Solving: Ea ≈ 52.8 kJ/mol.
Q.19Medium
For the equilibrium PCl₅(g) ⇌ PCl₃(g) + Cl₂(g), Kc = 1.8 at 298 K. If initial concentration of PCl₅ is 1 M, find [PCl₃] at equilibrium when dissociation is 30%.
Answer: A
If 30% of PCl₅ dissociates, [PCl₃] = 1 × 0.30 = 0.3 M and [Cl₂] = 0.3 M.
Q.20Medium
The hydration enthalpy of an ion depends on which of the following factors?
Answer: A
Hydration enthalpy depends on the charge density of the ion (charge/size ratio). Higher charge and smaller size lead to greater hydration enthalpy.
