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158 Q 3 Subjects 12th (PCM)
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Q.21 Easy JEE Chemistry 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.22 Easy JEE Chemistry 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.23 Easy JEE Chemistry 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.24 Easy JEE Chemistry 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.25 Easy JEE Chemistry 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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Q.26 Easy JEE Chemistry Chemical Kinetics
For the reaction: A + B → Products with Rate = k[A][B]², what is the overall order of reaction?
A 1
B 2
C 3
D 4
Correct Answer:  C. 3
EXPLANATION

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

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Q.27 Easy JEE Chemistry Chemical Kinetics
In a reaction mechanism with fast pre-equilibrium followed by slow step, which statement is correct?
A The slow step determines the overall rate
B The fast step determines the overall rate
C Both steps equally contribute to rate
D The mechanism cannot be determined from rate law
Correct Answer:  A. The slow step determines the overall rate
EXPLANATION

The rate-determining step (slowest step) controls the overall reaction rate, regardless of how many fast equilibrium steps precede it

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Q.28 Easy JEE Chemistry Chemical Kinetics
A zero-order reaction has an initial concentration of 0.5 M and rate constant k = 0.02 M/s. The time taken for the concentration to reduce to 0.1 M is:
A 10 s
B 15 s
C 20 s
D 25 s
Correct Answer:  C. 20 s
EXPLANATION

For zero-order reaction: [A]₀ - [A]ₜ = kt. So 0.5 - 0.1 = 0.02 × t, giving t = 20 s

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Q.29 Easy JEE Chemistry Chemical Kinetics
For the reaction 2NO + Cl₂ → 2NOCl, the rate law is found to be Rate = k[NO]²[Cl₂]. The order with respect to NO is:
A First order
B Second order
C Third order
D Negative order
Correct Answer:  B. Second order
EXPLANATION

The exponent of [NO] in the rate law is 2, making the reaction second order with respect to NO

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Q.30 Easy JEE Chemistry Chemical Kinetics
The collision theory of reaction rates explains that a reaction occurs when molecules collide with:
A Any energy
B Proper orientation and sufficient energy (≥ Eₐ)
C Maximum possible kinetic energy
D Random orientations
Correct Answer:  B. Proper orientation and sufficient energy (≥ Eₐ)
EXPLANATION

According to collision theory, collisions must have both proper spatial orientation and energy ≥ activation energy to result in a reaction.

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