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

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Topics in JEE Chemistry

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

Q.1 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

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Q.2 Easy Chemical Kinetics

Consider the mechanism: (1) A + B ⇌ C (fast equilibrium), (2) C + D → E + F (slow). Which is the rate-determining step?

A Step 1

B Step 2

C Both steps

D Cannot be determined

Correct Answer: B. Step 2

EXPLANATION

The slowest step in a mechanism is the rate-determining step (RDS), which is step 2

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Q.3 Easy Chemical Kinetics

For a zero-order reaction, the integrated rate law is [A] = [A]₀ - kt. If [A]₀ = 0.5 M and k = 0.02 M·s⁻¹, find time when [A] = 0

A 15 s

B 20 s

C 25 s

D 30 s

Correct Answer: C. 25 s

EXPLANATION

0 = 0.5 - 0.02t; t = 0.5/0.02 = 25 s

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Q.4 Easy Chemical Kinetics

Which of the following statements about collision theory is INCORRECT?

A Molecules must collide with proper orientation

B All collisions lead to reaction

C Collision frequency increases with temperature

D Only collisions with energy ≥ Eₐ are effective

Correct Answer: B. All collisions lead to reaction

EXPLANATION

Not all collisions are effective; only those with proper orientation and sufficient energy lead to reaction

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Q.5 Easy Chemical Kinetics

Half-life of a first-order reaction is 30 minutes. What fraction of reactant remains after 90 minutes?

A 1/2

B 1/4

C 1/8

D 1/16

Correct Answer: C. 1/8

EXPLANATION

After 90 min = 3 half-lives, remaining = (1/2)³ = 1/8

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Q.6 Easy Chemical Kinetics

For the reaction 2NO + O₂ → 2NO₂, the rate law is Rate = k[NO]²[O₂]. What is the overall order of reaction?

A First order

B Second order

C Third order

D Zero order

Correct Answer: C. Third order

EXPLANATION

Overall order = sum of exponents in rate law = 2 + 1 = 3 (third order)

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Q.7 Easy Chemical Kinetics

For an elementary reaction: A + A + 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, the rate law is determined by the stoichiometry: Rate = k[A]²[B], as 2 A molecules and 1 B molecule participate

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Q.8 Easy Chemical Kinetics

For the reaction A → B, experimental data shows: [A] vs time is a straight line. This indicates:

A First-order reaction

B Zero-order reaction

C Second-order reaction

D Third-order reaction

Correct Answer: B. Zero-order reaction

EXPLANATION

A straight line in [A] vs time plot indicates [A] = [A]₀ - kt, which is the integrated rate law for zero-order reactions

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Q.9 Easy Chemical Kinetics

For a reaction with rate law Rate = k[A]⁰[B]¹, if [B] is increased 4 times while [A] remains constant, the rate increases by:

A 2 times

B 4 times

C 8 times

D 16 times

Correct Answer: B. 4 times

EXPLANATION

Since the reaction is first-order in B and zero-order in A, Rate ∝ [B]. Increasing [B] by 4 times increases Rate by 4 times

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Q.10 Easy Chemical Kinetics

A catalyst increases the rate of reaction by:

A Increasing activation energy

B Providing an alternative reaction pathway with lower activation energy

C Increasing the frequency factor

D Changing the equilibrium constant

Correct Answer: B. Providing an alternative reaction pathway with lower activation energy

EXPLANATION

A catalyst works by providing an alternative mechanism with lower Ea, thus increasing reaction rate without being consumed

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