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JEE Chemistry

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

143 Q 5 Topics Take Test
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Topics in JEE Chemistry
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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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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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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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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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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Which of the following statements about activation energy (Eₐ) is correct?
A It is always positive and independent of temperature
B It depends on the direction of the reaction
C It is the minimum energy required for reactants to form products
D It is the total energy of reactants
Correct Answer:  C. It is the minimum energy required for reactants to form products
EXPLANATION

Activation energy is the minimum energy required for reactants to overcome the energy barrier and form products. It is always positive and independent of temperature.

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A reaction has a rate constant of k = 2.5 × 10⁻⁴ s⁻¹ at 298 K. What is the order of this reaction if the units of k are s⁻¹?
A Zero order
B First order
C Second order
D Third order
Correct Answer:  B. First order
EXPLANATION

The units s⁻¹ or time⁻¹ indicate a first-order reaction. For first-order reactions, the rate constant has units of time⁻¹.

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The half-life of a zero-order reaction is:
A Independent of initial concentration
B Directly proportional to initial concentration
C Inversely proportional to initial concentration
D Logarithmic with respect to initial concentration
Correct Answer:  B. Directly proportional to initial concentration
EXPLANATION

For a zero-order reaction, t₁/₂ = [A]₀/(2k), which is directly proportional to initial concentration.

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The rate of a chemical reaction is defined as the change in concentration of reactants or products per unit time. Which of the following is NOT a factor affecting reaction rate?
A Temperature of the system
B Nature of reactants and products
C Color of the reaction vessel
D Concentration of reactants
Correct Answer:  C. Color of the reaction vessel
EXPLANATION

The color of the reaction vessel does not affect the reaction rate. Temperature, nature of reactants, concentration, pressure, and catalyst are actual factors affecting reaction rate.

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Which factor does NOT significantly affect the conductance of an electrolytic solution?
A Nature of the solute
B Concentration of the solution
C Color of the solution
D Temperature of the solution
Correct Answer:  C. Color of the solution
EXPLANATION

Color of a solution is a physical property unrelated to ionic conductance. Conductance depends on nature of solute, concentration, temperature, and solvent.

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