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.
Which of the following is true for an endothermic reaction?
Answer: B
In endothermic reactions, ΔH is positive because heat is absorbed from surroundings. The system absorbs energy.
Q.42Medium
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.43Medium
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.
Q.44Medium
In electrochemistry, what does the cell potential (E°cell) indicate?
Answer: B
E°cell is directly related to the maximum electrical work (w_max = -nFE°cell) that can be obtained from a galvanic cell.
Q.45Easy
A solution has pH = 4. What is the concentration of H⁺ ions?
Answer: A
pH = -log[H⁺], so [H⁺] = 10⁻ᵖᴴ = 10⁻⁴ = 1 × 10⁻⁴ M.
Q.46Medium
For a reversible adiabatic process of an ideal gas, which statement is correct?
Answer: A
For a reversible adiabatic process, q = 0 and ΔS = 0 because there is no heat exchange and the process is reversible, making it isentropic.
Q.47Medium
The standard cell potential for a cell is E° = 1.10 V. Calculate ΔG° (F = 96500 C/mol, n = 2):
For the reaction: A → B, if the order is 2 and rate constant k = 0.5 L·mol⁻¹·s⁻¹, find the half-life when initial concentration is 2 M.
Answer: A
For a second-order reaction, the half-life depends inversely on both the rate constant and the initial concentration.
Step 1: [Identify the Reaction Order and Given Data]
We are dealing with a second-order reaction (order = 2) with rate constant k = 0.5 L·mol⁻¹·s⁻¹ and initial concentration [A]₀ = 2 M. We need to find the time required for the concentration to reduce to half its initial value.
Order=2,k=0.5 L⋅mol−1⋅s−1,[A]0=2 M
Step 2: [Apply the Half-Life Formula for Second-Order Reaction]
For a second-order reaction, the half-life formula is derived from the integrated rate law and is expressed as:
t1/2=k[A]01
Substituting the values:
t1/2=0.5×21=1.01=1.0 s
The half-life is 1.0 s, so the answer is (A).
Q.49Medium
What is the entropy change when 18 g of ice at 273 K is converted to water at 273 K? (ΔfusH = 6 kJ/mol)
Answer: A
ΔS = ΔH/T = (6000 J/mol) / 273 K = 22.0 J/(mol·K). For 18 g (1 mole) of ice, ΔS = 22.0 J/K.
Q.50Medium
A buffer solution contains 0.1 M acetic acid and 0.1 M sodium acetate. If Ka = 1.8 × 10⁻⁵, calculate the pH:
In electrolysis, if 2 moles of electrons are transferred, how many moles of Cu will be deposited from CuSO₄ solution? (Atomic mass of Cu = 64)
Answer: A
Cu²⁺ + 2e⁻ → Cu. For deposition of 1 mole Cu, 2 moles of electrons are required. So 2 moles e⁻ deposits 1 mole Cu.
Q.52Easy
At 298 K, the vapor pressure of water is 23.8 mmHg. What is the mole fraction of water vapor in saturated air at this temperature?
Answer: A
Mole fraction = vapor pressure of water / total atmospheric pressure = 23.7608 = 0.0313
Q.53Easy
For the reaction: N₂O₄(g) ⇌ 2NO₂(g), ΔH = 58 kJ/mol. If pressure is increased at constant temperature, the equilibrium will:
Answer: B
Increasing pressure favors the side with fewer moles of gas. 1 mole N₂O₄ ⇌ 2 moles NO₂. Equilibrium shifts left.
Q.54Easy
Which electrochemical cell cannot be recharged?
Answer: B
Daniell cell is a primary cell (non-rechargeable). Others are secondary (rechargeable) cells.
Q.55Easy
At 273 K, 1 mole of an ideal gas occupies 22.4 L. What will be its volume at 546 K and same pressure?
Answer: B
Using Charles's Law: V₁/T₁ = V₂/T₂ → V₂ = V₁ × (T₂/T₁) = 22.4 × (273546) = 44.8 L
Q.56Easy
The rate constant for a first-order reaction is 0.693 min⁻¹. What is its half-life?
Answer: B
For first-order reaction: t₁/₂ = 0.693/k = 0.0693.693 = 1 min
Q.57Easy
When 50 mL of 0.1 M HCl is mixed with 50 mL of 0.1 M NaOH, the resulting solution will have:
Answer: A
Equivalent moles of strong acid and strong base neutralize completely. The salt NaCl formed doesn't hydrolyze. pH = 7
Q.58Medium
The osmotic pressure of a solution is given by π = iMRT. If 0.1 M glucose solution has osmotic pressure 2.46 atm at 273 K, what is the van't Hoff factor?
Answer: B
i = π/(MRT) = 2.46/(0.1 × 0.0821 × 273) ≈ 1. Glucose is non-electrolyte with i = 1
Q.59Medium
For the exothermic reaction: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g), increasing temperature will:
Answer: B
For exothermic reactions, increasing temperature decreases Kc (unfavorable) and shifts equilibrium left (Le Chatelier's principle).
Q.60Medium
A buffer solution is prepared by mixing 100 mL of 0.1 M CH₃COOH and 100 mL of 0.1 M CH₃COONa. The pKa of acetic acid is 4.74. What is the pH?
