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.
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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?
