Chemical Kinetics Important Mcqs FPSC Chemistry

Chemical Kinetics Important Mcqs FPSC

What is the primary focus of chemical kinetics?
a) Energy changes in reactions
b) Reaction rates
c) Equilibrium positions
d) Bond formation
Answer: b) Reaction rates

Which of the following is NOT studied in chemical kinetics?
a) Speed of a reaction
b) Effect of catalysts
c) Whether a reaction is exothermic
d) Rate laws
Answer: c) Whether a reaction is exothermic
For the reaction 2N2O5→4NO2+O2, if [O2] increases by 0.5 M/s, what is the rate of N2O5 consumption?
a) 1.0 M/s
b) 2.0 M/s
c) 0.25 M/s
d) 0.5 M/s
Answer: b) 2.0 M/s
The rate of disappearance of a reactant is always:
a) Positive
b) Negative
c) Zero
d) Equal to the rate of product formation
Answer: b) Negative
Which term describes the equation (Rate = k[A]^m[B]^n)?
a) Rate constant
b) Rate law
c) Rate expression
d) Equilibrium constant
Answer: b) Rate law
Reaction orders are determined by:
a) Stoichiometric coefficients
b) Experimental data
c) Temperature
d) Activation energy
Answer: b) Experimental data
A reaction with rate law (Rate = k[A]^2) is:
a) Zero-order in A
b) First-order in A
c) Second-order in A
d) Third-order overall
Answer: c) Second-order in A
The units of the rate constant for a zero-order reaction are:
a) M/s
b) 1/s
c) M⁻¹s⁻¹
d) M²/s
Answer: a) M/s
Which graph is linear for a first-order reaction?
a) ([A]) vs. time
b) (\ln[A]) vs. time
c) (1/[A]) vs. time
d) ([A]^2) vs. time
Answer: b) (\ln[A]) vs. time
The half-life of a first-order reaction depends on:
a) Initial concentration
b) Rate constant
c) Temperature
d) Both b and c
Answer: b) Rate constant
In a reaction coordinate diagram, the highest point represents the:
a) Reactants
b) Products
c) Transition state
d) Intermediate
Answer: c) Transition state
A negative (Delta H) indicates a/an:
a) Endothermic reaction
b) Exothermic reaction
c) Isothermic reaction
d) Catalyzed reaction
Answer: b) Exothermic reaction
Activation energy ((Ea)) is the energy difference between:
a) Reactants and products
b) Reactants and transition state
c) Products and intermediates
d) Two intermediates
Answer: b) Reactants and transition state
Catalysts increase reaction rates by:
a) Lowering activation energy
b) Increasing (\Delta H)
c) Shifting equilibrium
d) Being consumed
Answer: a) Lowering activation energy
Which step determines the overall rate in a multi-step mechanism?
a) Fastest step
b) Slowest step
c) First step
d) Last step
Answer: b) Slowest step
Collision theory states that reactions require:
a) High pressure
b) Correct orientation and sufficient energy
c) Low temperature
d) Solid catalysts
Answer: b) Correct orientation and sufficient energy
The Arrhenius equation relates (k) to:
a) (Ea) and (T)
b) (Delta H)
c) Concentration
d) Pressure
Answer: a) (Ea) and (T)
Increasing temperature generally:
a) Decreases reaction rate
b) Increases activation energy
c) Increases reaction rate
d) Has no effect
Answer: c) Increases reaction rate
An intermediate in a reaction mechanism is:
a) A catalyst
b) A final product
c) Formed and consumed during the reaction
d) Present in the rate law
Answer: c) Formed and consumed during the reaction
For the rate law (Rate = k[A][B]^0), the reaction order is:
a) Zero
b) First
c) Second
d) Third
Answer: b) First
Which is true about catalysts?
a) They shift equilibrium
b) They are consumed
c) They lower (Ea)
d) They change (Delta H)
Answer: c) They lower (Ea)
A reaction with a rate constant of k=0.05M−1s−1 is::
a) Zero-order
b) First-order
c) Second-order
d) Third-order
Answer: c) Second-order
The integrated rate law for a second-order reaction is:
a) ([A]_t = -kt + [A]_0)
b) (\ln[A]_t = -kt + \ln[A]_0)
c) (1/[A]_t = kt + 1/[A]_0)
d) None of the above
Answer: c) (1/[A]_t = kt + 1/[A]_0)
In a zero-order reaction, doubling the concentration of reactant:
a) Doubles the rate
b) Halves the rate
c) Has no effect
d) Quadruples the rate
Answer: c) Has no effect
The slope of a (ln[A]) vs. time plot for a first-order reaction is:
a) (-k)
b) (k)
c) (1/k)
d) (\ln k)
Answer: a) (-k)
Which factor does NOT affect reaction rate?
a) Concentration
b) Temperature
c) Catalyst
d) Equilibrium constant
Answer: d) Equilibrium constant
A reaction mechanism consists of:
a) One elementary step
b) Multiple transition states
c) Overall balanced equation
d) All of the above
Answer: d) All of the above
The rate-determining step in a mechanism is the:
a) Fastest step
b) Step with highest (Ea)
c) Step with lowest (Ea)
d) Last step
Answer: b) Step with highest (Ea)
For the reaction (2A + B \rightarrow C), if tripling [A] doubles the rate, the order with respect to A is:
a) 0
b) 1
c) 2
d) 3
Answer: b) 1
For a reaction A→B, if the half-life is 20 s, what percentage of A remains after 60 s?
a) 25%
b) 12.5%
c) 50%
d) 6.25%
Answer: b) 12.5%
The rate law for (2A + B → C) is (Rate = k[A][B]). What is the overall order?
a) 0
b) 1
c) 2
d) 3
Answer: c) 2
Which statement about intermediates is FALSE?
a) They appear in the rate law
b) They are formed in one step and consumed in another
c) They are not present in the overall reaction
d) They have short lifetimes
Answer: a) They appear in the rate law
A reaction has the mechanism: Step 1 (slow): (A + B → C) Step 2 (fast): (C + D → E The rate law is:
a) (k[A][B])
b) (k[A][B][D])
c) (k[C][D])
d) (k[A][B][C][D])
Answer: a) (k[A][B])
A catalyst is regenerated:
a) In the first step
b) In the last step
c) Never
d) Throughout the reaction
Answer: d) Throughout the reaction
Which plot for a second-order reaction is linear?
a) ([A]) vs. (t)
b) (\ln[A]) vs. (t)
c) (1/[A]) vs. (t)
d) (\ln k) vs. (1/T)
Answer: c) (1/[A]) vs. (t)
The Arrhenius equation explains the effect of:
a) Concentration on rate
b) Temperature on (k)
c) Pressure on equilibrium
d) Catalysts on (\Delta H)
Answer: b) Temperature on (k)
If (k) increases by a factor of 3 when (T) rises from 300K to 310K, the reaction is:
a) Zero-order
b) First-order
c) Temperature-independent
d) Sensitive to temperature
Answer: d) Sensitive to temperature
For the reaction (A → B), the rate constant is 0.693 min−1. The half-life is:
a) 1 min
b) 2 min
c) 0.5 min
d) 0.1 min
Answer: a) 1 min
In a reaction coordinate diagram, (\Delta H) is:
a) (Ea forward}) – Ea reverse}))
b) Energy of products – Energy of reactants
c) Energy of transition state – Energy of reactants
d) None of the above
Answer: b) Energy of products – Energy of reactants
A reaction with ΔH = -50 kj is:
a) Endothermic
b) Exothermic
c) Isothermic
d) Catalyzed
Answer: b) Exothermic
Which step is the rate-determining step?
a) Fastest step
b) Step with intermediates
c) Step with highest (E_a)
d) Step with lowest (E_a)
Answer: c) Step with highest (E_a)
The frequency factor (A) in the Arrhenius equation represents:
a) Activation energy
b) Fraction of collisions with correct orientation
c) Temperature
d) Rate constant
Answer: b) Fraction of collisions with correct orientation
If the rate law is (Rate = k[A]^2), doubling [A] will:
a) Double the rate
b) Quadruple the rate
c) Not change the rate
d) Halve the rate
Answer: b) Quadruple the rate
A reaction is first-order in A and second-order in B. The rate law is:
a) (k[A][B])
b) (k[A]^2[B])
c) (k[A][B]^2)
d) (k[A]^2[B]^2)
Answer: c) (k[A][B]^2)
Which is NOT a requirement for effective collisions?
a) Sufficient energy
b) Correct orientation
c) High pressure
d) Collision between reactants
Answer: c) High pressure
The rate constant (k) for a reaction decreases when:
a) (E_a) increases
b) Temperature increases
c) Catalyst is added
d) Concentration increases
Answer: a) (E_a) increases
For the reaction (2NO_2 → 2NO + O_2), the rate of formation of (O_2) is 1.2 m/s. What is the rate of disappearance of (NO_2)?
a) 0.6 M/s
b) 1.2 M/s
c) 2.4 M/s
d) 3.6 M/s
Answer: c) 2.4 M/s
A zero-order reaction has a half-life of 10 s. If the initial concentration is 2 M, the rate constant is:
a) 0.1 M/s
b) 0.2 M/s
c) 0.05 M/s
d) 0.4 M/s
Answer: a) 0.1 M/s
The activation energy for the reverse reaction is:
a) Ea(forward)+ΔH
b) Ea(forward)−ΔH
c) ΔH−Ea(forward)
d) Unrelated to Ea(forward)Ea(forward)
Answer: a) Ea(forward)+ΔH
In a reaction mechanism, if the first step is fast and the second is slow, the rate law depends on:
a) First step
b) Second step
c) Both steps
d) Neither
Answer: b) Second step
A reaction with a rate law (Rate = k) is:
a) First-order
b) Second-order
c) Zero-order
d) Third-order
Answer: c) Zero-order
Which is true about the Arrhenius equation?
a) k∝T
b) k∝1/Ea
c) (k ∝ e^{-Ea/RT})
d) k∝ln⁡T
Answer: c) (k ∝ e^{-Ea/RT})
For a reaction with (\Delta H > 0), the reverse reaction has:
a) Higher (Ea) than forward
b) Lower (Ea) than forward
c) Same (Ea) as forward
d) No (Ea)
Answer: b) Lower (Ea) than forward
The rate constant of a reaction at 300K is 2×10−3 s−1. At 310K, it becomes (4 x 10^{-3} s-1. The activation energy is:
a) Positive
b) Negative
c) Zero
d) Cannot determine
Answer: a) Positive
If a reaction’s rate doubles when [A] is doubled and remains unchanged when [B] is doubled, the rate law is:
a) (k[A])
b) (k[B])
c) (k[A][B])
d) (k[A]^2)
Answer: a) (k[A])
Which is an example of a homogeneous catalyst?
a) Platinum in hydrogenation
b) Enzymes in digestion
c) (H^+) in ester hydrolysis
d) All of the above
Answer: c) (H^+) in ester hydrolysis
A reaction’s half-life increases as the reaction progresses. The reaction is:
a) Zero-order
b) First-order
c) Second-order
d) Third-order
Answer: c) Second-order
The rate-determining step in a mechanism determines:
a) The overall stoichiometry
b) The rate law
c) The activation energy
d) The intermediates
Answer: b) The rate law
A reaction with the rate law (Rate = k[NO]^2[O_2]) is:
a) First-order in NO, first-order overall
b) Second-order in NO, third-order overall
c) Second-order in NO, first-order overall
d) First-order in NO, second-order overall
Answer: b) Second-order in NO, third-order overall
For a reaction where (ln k) vs. (1/T) gives a straight line, the slope is:
a) (-Ea/R)
b) (Ea/R)
c) (-R/Ea)
d) (k)
Answer: a) (-Ea/R)
In the reaction (2A + B → C), if [A] is halved and [B] is doubled, the rate remains the same. The rate law is:
a) (k[A]^2[B])
b) (k[A][B])
c) (k[A]^2)
d) (k[B])
Answer: c) (k[A]^2)
Which statement about catalysts is FALSE?
a) They lower (E_a)
b) They are consumed
c) They speed up both forward and reverse reactions
d) They do not affect (\Delta H)
Answer: b) They are consumed
A reaction’s rate constant (k = 3.0×10−2 m−1s−1. The reaction order is:
a) 0
b) 1
c) 2
d) 3
Answer: c) 2
The rate law for (A + B → C) is (Rate = k[A]). The reaction is:
a) First-order in A, zero-order in B
b) Zero-order in A, first-order in B
c) First-order overall
d) Both a and c
Answer: d) Both a and c
If a reaction’s rate increases by a factor of 8 when [A] is doubled, the order with respect to A is:
a) 0
b) 1
c) 2
d) 3
Answer: d) 3
A reaction with a negative (\Delta H) and high (E_a) will be:
a) Spontaneous and fast
b) Non-spontaneous and slow
c) Spontaneous and slow
d) Non-spontaneous and fast
Answer: c) Spontaneous and slow
In a reaction mechanism, the molecularity of an elementary step is:
a) The number of reactants
b) The reaction order
c) The stoichiometric coefficients
d) Both a and c
Answer: d) Both a and c
For a reaction with the rate law (Rate = k[A]^{1/2}[B]), the overall order is:
a) 0.5
b) 1.5
c) 2
d) 1
Answer: b) 1.5
A reaction has ΔH=+60 kJ and Ea=80 kJ. The (Ea) for the reverse reaction is:
a) 20 kJ
b) 140 kJ
c) 80 kJ
d) 60 kJ
Answer: a) 20 kJ
The rate law (Rate = k[H^+][S2O3^{2-}]) suggests:
a) (H^+) is a catalyst
b) (H^+) is an intermediate
c) (H^+) is a reactant
d) (H^+) is a product
Answer: a) (H^+) is a catalyst
For the reaction (A → B), a plot of (1/[A]) vs. time is linear with slope (k). The order is:
a) 0
b) 1
c) 2
d) 3
Answer: c) 2
In the reaction (2A + B → C), tripling [A] and doubling [B] increases the rate by 12 times. The rate law is:
a) (k[A]^2[B])
b) (k[A][B]^2)
c) (k[A]^1[B]^1)
d) (k[A]^2[B]^1)
Answer: a) (k[A]^2[B])
A reaction follows the rate law (Rate = k). After 2 minutes, 50% of the reactant remains. How much remains after 4 minutes?
a) 25%
b) 0%
c) 50%
d) 75%
Answer: b) 0%
The activation energy of a reaction is (E_a). If the temperature is doubled, the rate constant:
a) Always doubles
b) Increases exponentially
c) Decreases
d) Depends on (E_a)
Answer: d) Depends on (E_a)
For a first-order reaction, if 75% of the reactant decomposes in 60 minutes, the rate constant is:
a) (0.0231 min−1
b) (0.0139 min−1
c) (0.0347 min−1
d) (0.0462 min−1 Answer: c) (0.0347 min−1
A reaction mechanism includes an intermediate. Which step CANNOT be the rate-determining step?
a) The step forming the intermediate
b) The step consuming the intermediate
c) Both steps
d) Neither step
Answer: b) The step consuming the intermediate
A reaction has two steps with (E_{a1} = 25kJ/mol and (E_{a2} = 40 25kJ/mol. The rate-determining step is:
a) Step 1
b) Step 2
c) Both steps
d) Cannot determine
Answer: b) Step 2
In a reaction, the concentration of an intermediate is:
a) Constant
b) Zero at equilibrium
c) Highest at the start
d) Highest during the reaction
Answer: d) Highest during the reaction
The rate law for (A + 2B \rightarrow C) is (Rate = k[A][B]). The molecularity of the rate-determining step is:
a) Unimolecular
b) Bimolecular
c) Termolecular
d) Cannot determine
Answer: b) Bimolecular
A reaction with a rate constant of (k = 5.0 x 10^{-3} M−2s−1) is:
a) Zero-order
b) First-order
c) Second-order
d) Third-order
Answer: d) Third-order
The rate law for a reaction is (Rate = k[X][Y]^2). If [X] is doubled and [Y] is halved, the rate becomes:
a) Half
b) Double
c) Same
d) Quadruple
Answer: a) Half
A catalyst is added to a reaction at equilibrium. The equilibrium constant:
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero
Answer: c) Remains the same
For the reaction (A \rightarrow B), the half-life is inversely proportional to [A]. The order is:
a) 0
b) 1
c) 2
d) 3
Answer: c) 2
The rate-determining step in a mechanism is the only step that:
a) Involves intermediates
b) Has the highest (E_a)
c) Is exothermic
d) Is reversible
Answer: b) Has the highest (E_a)
The rate law (Rate = k[O3][O]) suggests the reaction:
a) (O3 + O → 2O_2)
b) (O_3 → O_2 + O)
c) (2O_3 → 3O_2)
d) None of the above
Answer: a) (O_3 + O → 2O_2)
A reaction’s rate increases by a factor of 2.5 when [A] is increased by 1.5 times. The order with respect to A is:
a) 0
b) 1
c) 2
d) 1.5
Answer: d) 1.5
The rate constant (k) for a reaction at 25°C is (2.0 x 10^{-4} s-1. At 35°C, (k = 4.0 x 10^{-4} s-1 The activation energy is:
a) (52.9 kJ/mol
b) (29.5 kJ/mol
c) (105.8 kJ/mol
d) (10.6 kJ/mol
Answer: a) (52.9 kJ/mol
A reaction has the mechanism: Step 1: (A → B) (fast) Step 2: (B + C → D) (slow) The rate law is:
a) (k[A][C])
b) (k[B][C])
c) (k[A]^2[C])
d) (k[A][C]^2)
Answer: a) (k[A][C])
The half-life of a second-order reaction is 100 s when [A]₀ = 0.1 M. The rate constant is:
a) 0.01 M−1s−1
b) 0.1 M−1s−1
c) 1.0 M−1s−1
d) 10 M−1s−1
Answer: b) 0.1 M−1s−1
The rate law for the reaction (2A + B → C + D) is (Rate = k[A][B]). If [A] is doubled and [B] is constant, the rate:
a) Doubles
b) Quadruples
c) Halves
d) Remains the same
Answer: a) Doubles
A reaction with the rate law (Rate = k[A]^0[B]^2) has an overall order of:
a) 0
b) 1
c) 2
d) 3
Answer: c) 2
The activation energy for a reaction is calculated using:
a) The Arrhenius equation
b) The integrated rate law
c) The rate law
d) Collision theory
Answer: a) The Arrhenius equation
In a reaction mechanism, the rate law is determined by:
a) The fastest step
b) The stoichiometric coefficients
c) The slowest step
d) The overall reaction
Answer: c) The slowest step

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