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

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Difficulty: All Easy Medium Hard 1–10 of 457

Topics in JEE Chemistry

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

Q.1 Hard Chemical Kinetics

A reaction has Eₐ = 60 kJ/mol. How many times faster will it be at 327°C compared to 27°C? (R = 8.314 J/mol·K, assume A constant)

A 100 times

B 256 times

C 500 times

D 1000 times

Correct Answer: C. 500 times

EXPLANATION

Using ln(k₂/k₁) = (Eₐ/R)[(T₂-T₁)/(T₁T₂)]; ln(k₂/k₁) = (60000/8.314)[(300)/(600×300)] ≈ 6.2; k₂/k₁ ≈ 500

Test

Q.2 Medium Chemical Kinetics

The half-life of a second-order reaction is 100 s when initial concentration is 0.5 M. What is the rate constant?

A 0.04 M⁻¹s⁻¹

B 0.02 M⁻¹s⁻¹

C 0.2 M⁻¹s⁻¹

D 0.01 M⁻¹s⁻¹

Correct Answer: A. 0.04 M⁻¹s⁻¹

EXPLANATION

For second-order: t₁/₂ = 1/(k[A]₀); 100 = 1/(k × 0.5); k = 0.04 M⁻¹s⁻¹

Test

Q.3 Hard Chemical Kinetics

For the reaction: (1) Cl₂ ⇌ 2Cl (fast), (2) Cl + H₂ → HCl + H (slow), (3) H + Cl₂ → HCl + Cl (fast). The overall reaction is:

A Cl₂ + H₂ → 2HCl

B 2Cl₂ + H₂ → 2HCl + Cl

C H₂ + Cl₂ → 2HCl

D Cl + H₂ → HCl + H

Correct Answer: A. Cl₂ + H₂ → 2HCl

EXPLANATION

Adding all steps and canceling intermediates (Cl, H): Cl₂ + H₂ → 2HCl

Test

Q.4 Medium Chemical Kinetics

The integrated rate law for second-order reaction is 1/[A] = 1/[A]₀ + kt. If [A]₀ = 0.5 M, k = 0.4 M⁻¹s⁻¹, find [A] after 5 seconds

A 0.2 M

B 0.25 M

C 0.1 M

D 0.15 M

Correct Answer: B. 0.25 M

EXPLANATION

1/[A] = 2 + 0.4(5) = 2 + 2 = 4; [A] = 1/4 = 0.25 M

Test

Q.5 Medium Chemical Kinetics

Which statement about potential energy diagrams is CORRECT?

A Higher activation energy means faster reaction

B An exothermic reaction has ΔH > 0

C Activation energy is always greater than ΔH

D Catalyst changes activation energy but not ΔH

Correct Answer: D. Catalyst changes activation energy but not ΔH

EXPLANATION

Catalyst lowers Eₐ (forward and reverse) without changing ΔH, reaction enthalpy change

Test

Q.6 Medium Chemical Kinetics

For an elementary reaction: 2A + B → Products, the rate law is:

A Rate = k[A][B]

B Rate = k[A]²[B]

C Rate = k[A][B]²

D Rate = k[A]³[B]

Correct Answer: B. Rate = k[A]²[B]

EXPLANATION

For elementary reactions, rate law exponents = stoichiometric coefficients. Rate = k[A]²[B]

Test

Q.7 Hard Chemical Kinetics

For a reaction with Eₐ = 50 kJ/mol and A = 2 × 10¹³ s⁻¹ (Arrhenius pre-exponential factor), calculate k at 300K (R = 8.314 J/mol·K)

A 2.3 × 10⁻² s⁻¹

B 1.8 × 10⁻¹ s⁻¹

C 3.4 × 10⁻³ s⁻¹

D 5.1 × 10⁻² s⁻¹

Correct Answer: C. 3.4 × 10⁻³ s⁻¹

EXPLANATION

k = A·exp(-Eₐ/RT) = 2 × 10¹³ × exp(-50000/8.314×300) = 2 × 10¹³ × exp(-20.03) ≈ 3.4 × 10⁻³ s⁻¹

Test

Q.8 Easy Chemical Kinetics

Which factor does NOT affect the rate constant k of a reaction?

A Temperature

B Concentration of reactants

C Nature of reactants

D Presence of catalyst

Correct Answer: B. Concentration of reactants

EXPLANATION

Rate constant k is independent of reactant concentration; it depends on T, nature of reactants, and catalyst

Test

Q.9 Medium Chemical Kinetics

In the reaction A → Products, doubling [A] increases rate by 4 times. The order of reaction is:

A Zero

B First

C Second

D Third

Correct Answer: C. Second

EXPLANATION

If doubling concentration increases rate by 4 times (2²), reaction is second order

Test

Q.10 Medium Chemical Kinetics

The decomposition of N₂O₅ is a first-order reaction. If 50% decomposes in 30 minutes, what is the rate constant?

A 0.023 min⁻¹

B 0.035 min⁻¹

C 0.052 min⁻¹

D 0.069 min⁻¹

Correct Answer: A. 0.023 min⁻¹

EXPLANATION

For first-order: k = 0.693/t₁/₂ = 0.693/30 = 0.0231 min⁻¹ ≈ 0.023 min⁻¹

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