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.
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.
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.
