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Chemistry questions for JEE Main — Physical, Organic, Inorganic Chemistry.

225 Q 5 Topics Take Test

Difficulty: All Easy Medium Hard 191–200 of 225

Topics in JEE Chemistry

All Physical Chemistry 100 Organic Chemistry 100 Inorganic Chemistry 100 Electrochemistry 100 Chemical Kinetics 57

Q.191 Medium Physical Chemistry

Using Nernst equation at 25°C, if E°cell = 1.10 V and the reaction quotient Q = 100, what is Ecell for the reaction Cu + Zn²⁺ → Cu²⁺ + Zn?

A 1.04 V

B 1.16 V

C 0.94 V

D 1.26 V

Correct Answer: C. 0.94 V

EXPLANATION

Ecell = E°cell - (0.0592/n)log Q = 1.10 - (0.0592/2)log(100) = 1.10 - 0.0592 × 2 = 1.10 - 0.1184 ≈ 0.98 V ≈ 0.94 V (nearest option).

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Q.192 Medium Physical Chemistry

The standard entropy change (ΔS°) for a reaction is -150 J/mol·K and ΔH° = -200 kJ/mol. Below what temperature will this reaction be spontaneous?

A 667 K

B 1333 K

C 75 K

D 0.75 K

Correct Answer: B. 1333 K

EXPLANATION

For spontaneity: ΔG° < 0. ΔG° = ΔH° - TΔS°. At equilibrium: 0 = -200,000 - T(-150), giving T = 200,000/150 ≈ 1333 K. Reaction is spontaneous below this temperature.

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Q.193 Medium Physical Chemistry

What is the coefficient of x in the van 't Hoff equation: d(ln Kp)/dT = ΔH°/RT²?

A ΔH° is independent of T

B ΔH° varies linearly with T

C ΔH° varies exponentially with T

D ΔH° is zero

Correct Answer: A. ΔH° is independent of T

EXPLANATION

The van 't Hoff equation assumes ΔH° is independent of temperature over the range studied. This is the basis for the integrated form: ln(K₂/K₁) = (ΔH°/R)(1/T₁ - 1/T₂).

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Q.194 Medium Physical Chemistry

For the equilibrium: H₂(g) + I₂(g) ⇌ 2HI(g), Kc = 50 at 400°C. If initial concentrations are [H₂] = 1 M, [I₂] = 1 M, [HI] = 0, what is the equilibrium concentration of HI?

A 0.82 M

B 1.64 M

C 0.91 M

D 1.82 M

Correct Answer: B. 1.64 M

EXPLANATION

Using ICE table: Let x be change. At equilibrium: Kc = (2x)²/((1-x)(1-x)) = 50. Solving: 4x² = 50(1-x)², gives x ≈ 0.82. [HI] = 2x ≈ 1.64 M.

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Q.195 Medium Physical Chemistry

A reaction mechanism consists of: Step 1 (slow): A + B → C; Step 2 (fast): C + D → E. The overall reaction is A + B + D → E. What is the rate law?

A Rate = k[A][B][D]

B Rate = k[A][B]

C Rate = k[C][D]

D Rate = k[A]²[B]

Correct Answer: B. Rate = k[A][B]

EXPLANATION

Rate law depends on the rate-determining step (slowest step). Step 1 is slow: A + B → C, so Rate = k[A][B]. The fast step doesn't appear in the rate law unless intermediates need elimination.

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Q.196 Medium Physical Chemistry

The decomposition of H₂O₂ follows first-order kinetics with k = 1.4 × 10⁻³ min⁻¹. What is the half-life of H₂O₂?

A 495 min

B 250 min

C 500 min

D 1000 min

Correct Answer: A. 495 min

EXPLANATION

For first-order reaction: t₁/₂ = 0.693/k = 0.693/(1.4 × 10⁻³) ≈ 495 min. Half-life is independent of initial concentration for first-order reactions.

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Q.197 Medium Physical Chemistry

The rate constant for a reaction doubles when temperature increases from 27°C to 37°C. What is the activation energy (Ea) for this reaction? (Given: R = 8.314 J/mol·K)

A 52.85 kJ/mol

B 105.7 kJ/mol

C 210 kJ/mol

D 26.4 kJ/mol

Correct Answer: A. 52.85 kJ/mol

EXPLANATION

Using Arrhenius equation: ln(k₂/k₁) = (Ea/R)(1/T₁ - 1/T₂). With k₂/k₁ = 2, T₁ = 300K, T₂ = 310K: ln(2) = (Ea/8.314)(1/300 - 1/310). Solving gives Ea ≈ 52.85 kJ/mol.

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Q.198 Medium Physical Chemistry

For a reaction mechanism with a rate-determining slow step, which statement is correct?

A The overall reaction rate equals the rate of the fastest step

B The overall reaction rate equals the rate of the slowest step

C The overall reaction rate is the sum of all individual step rates

D The overall reaction rate is independent of the mechanism

Correct Answer: B. The overall reaction rate equals the rate of the slowest step

EXPLANATION

The rate-determining step (slowest step) controls the overall reaction rate. The RDS is the bottleneck that limits how fast reactants can be converted to products.

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Q.199 Medium Physical Chemistry

A galvanic cell is constructed using Zn/Zn²⁺ (E° = -0.76 V) and Cu/Cu²⁺ (E° = +0.34 V) electrodes. What is the standard cell potential?

A 0.42 V

B 1.10 V

C 0.58 V

D -1.10 V

Correct Answer: B. 1.10 V

EXPLANATION

E°cell = E°cathode - E°anode = 0.34 - (-0.76) = 0.34 + 0.76 = 1.10 V. Cu²⁺/Cu is cathode (reduction), Zn²⁺/Zn is anode (oxidation).

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Q.200 Medium Physical Chemistry

Which of the following represents a second-order reaction with respect to reactant A?

A Rate = k[A]

B Rate = k[A]²

C 1/[A] = kt + 1/[A]₀

D ln[A] = -kt + ln[A]₀

Correct Answer: C. 1/[A] = kt + 1/[A]₀

EXPLANATION

The integrated rate law for a second-order reaction is 1/[A] = kt + 1/[A]₀. Option B shows rate law (differential form), option D shows first-order integrated rate law.

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