Chemical Kinetics Mock Test – NEET Chemistry

1. A reaction

occurs in a closed constant-volume vessel.
The normalized reaction rate is experimentally zero order over the stated composition range:

Initially,

There are no competing reactions and no replenishment of either reactant.
Assume the zero-order rate remains valid while both reactants are present and the reaction stops when the limiting reactant is exhausted.
Which conclusion is correct?

2. A first-order reaction is studied at two temperatures, and . Its rate constants are

and

Two identical solutions initially contain

Experiment X is conducted at for 10 min and then at for another 10 min.
Experiment Y is conducted at for 10 min and then at for another 10 min.
Temperature changes are instantaneous, and no reaction occurs during the changes. Assume first-order kinetics at both temperatures.
Which pair gives the final concentration of A in either experiment and the ratio of the instantaneous disappearance rates immediately after the temperature changes at ?

3. Four reactions are studied under different kinetic conditions.
Their experimentally observed rate laws are given below:

Assume conventional concentration-based reaction-rate units and an unchanged applicable rate law in each case.
Consider the following statements.
Statement I: Reactions I and II have the same overall order, despite having different partial orders.
Statement II: Reactions I and II have rate constants with the same dimensions.
Statement III: Reaction III must involve zero molecules in its rate-determining elementary step because its overall order is zero.
Statement IV: Reaction IV could represent an elementary bimolecular event, but its observed rate law alone does not prove that the overall reaction is elementary.
Statement V: The negative partial order in Reaction II requires B to appear on the product side of its balanced chemical equation.
Which combination is correct?

4. For the reaction , the concentration–time graph of A is described below.

Which pair correctly gives the instantaneous rate of appearance of P and the normalized reaction rate at , respectively? Both values are in .

5. A reaction at constant temperature follows the experimentally determined rate law

At one instant, the concentrations are , and . The measured reaction rate is .
Which pair gives the overall reaction order and the rate constant with appropriate units?

6. A reversible reaction occurs through elementary forward and reverse steps:

The forward and reverse rates are

and

The net forward rate is defined as .
Consider the following statements.
Statement I: At fixed P concentration, the net forward rate need not be directly proportional to A concentration.
Statement II: At equilibrium, the net reaction rate is zero, although the individual forward and reverse rates can both be non-zero.
Statement III: The net rate can become negative even when both elementary rate constants remain positive.
Statement IV: Because both elementary steps are first order, the net forward rate must be expressible as , with a composition-independent , for every positive A and P concentration.
Which combination is correct?

7. A gaseous reactant A undergoes the first-order decomposition

in a closed movable-piston vessel at constant temperature and total pressure.
Initially, the vessel contains only A.
The experimentally established local disappearance law is

where is the instantaneous vessel volume.
Assume ideal-gas behaviour, no leakage and an unchanged positive rate constant.
Consider the following statements.
Statement I: The amount of unreacted A follows an exponential first-order decay law.
Statement II: After the first half-life of A in terms of amount remaining, its concentration is one-third of its initial concentration.
Statement III: Because the amount of A follows first-order kinetics, a plot of against time must be a straight line with slope despite expansion of the vessel.
Statement IV: At the first half-life in terms of amount remaining, the vessel volume is times its initial volume.
Which combination is correct?

8. A reversible reaction is investigated at a fixed temperature:

A solid catalyst accelerates the reaction through an alternative surface pathway.
Under conditions where all active catalytic sites are occupied, the observed rate contribution from this surface pathway is proportional to the available active surface area.
Initially, the catalyst has an active surface area of

Its activity is subsequently modified in two stages.
First, an additional catalyst portion is introduced, doubling the total available surface area.
Next, an inhibitor adsorbs onto the catalyst and blocks of the enlarged surface.
The inhibitor does not change the energy barrier of the remaining active sites.
Assume the solution composition, temperature and surface activity per unblocked site are otherwise unchanged during these instantaneous adjustments.
Which pair gives the final active surface area and the ratio of the final to initial catalytic rate contributions?

9. A gaseous reactant A undergoes the first-order decomposition

in a rigid vessel at constant temperature. Initially, the vessel contains A and an inert gas, but their individual partial pressures are unknown. No B is initially present.
The following total pressures are measured:

Assume ideal-gas behaviour and unchanged first-order kinetics.
Which pair gives the initial partial pressure of A and the predicted total pressure after 30 min?

10. A second-order reaction obeys

A rate constant is reported as .
A student wishes to express concentrations in , time in seconds, and reaction rate in .
Which pair correctly gives the numerical value of the rate constant in the new units and the reaction rate at ?

11. A reaction occurs according to

at constant temperature and volume.
The experimentally established normalized rate law is

Initially,

After 10 min, of A has decomposed.
Assuming the stated kinetic law remains valid, which pair gives the half-life of A and the instantaneous rate of appearance of P at ?
Use .

12. A pure gaseous reactant A decomposes according to

The amount of A follows first-order disappearance kinetics.
The reaction occurs in an ideal-gas vessel fitted with a movable piston, maintaining constant temperature and total pressure.
The initial gas volume is

After 10 min, the gas volume is

No gas enters or escapes.
Which pair gives the time at which the gas volume becomes and the mole fraction of A at that instant?

13. A complex reaction proceeds through:
Step 1 (fast equilibrium):

Step 2 (slow):

At one instant, , and . The measured instantaneous rate of formation of P is .
Assume that the fast equilibrium is maintained and the slow step controls product formation.
At another instant at the same temperature, and .
What rate of formation of P is predicted?

14. The overall gaseous reaction

is proposed to occur through the following mechanism:
Step 1 (fast equilibrium):

Step 2 (slow):

Assume that the first step establishes a rapid equilibrium and that the second step determines the overall reaction rate. Which rate law is consistent with this mechanism?

15. The same gaseous reaction is investigated at fixed temperature and follows the experimentally established concentration-based rate law

where is expressed in .
An experimenter instead expresses the rate of disappearance of A using its partial pressure and writes

The balanced overall reaction is

and the gas behaves ideally at constant temperature and volume.
If and , what is the value of ?

16. Reaction X follows zero-order disappearance:

with

Reaction Y follows first-order disappearance:

with

Initially,

Both reactions occur independently at constant temperature and volume.
At what time do their instantaneous disappearance rates become equal, and what is the concentration of X at that instant?
Use .

17. A reaction

is studied in a constant-volume vessel at fixed temperature.
Over the investigated concentration range, its experimentally established rate law is

Initially,

Product P is stable, and no other reaction occurs.
At a later instant, half the initial amount of A has been consumed.
Assume the stated rate law remains valid throughout this interval.
Which pair gives the ratio of the later instantaneous rate to the initial rate and the overall reaction order?

18. A gaseous reaction is investigated at two temperatures, and , with .
The activation-energy threshold and molecular structure are assumed unchanged.
A separate catalyst experiment is performed at .
The observations are:

The total encounter frequency is identical under all three stipulated conditions.
Assume that satisfying both criteria is sufficient for an effective collision and that the supplied fractions refer to the relevant pathway in each condition.
Which pair gives the ratio of effective-collision frequencies in Conditions II and III relative to Condition I?

19. A chemical reaction is represented by the general equation

where are the smallest positive whole-number stoichiometric coefficients.
The reaction takes place at constant temperature and volume.
During a 5.0-minute observation interval, the following average concentration-change rates are measured:

The concentration of D at the beginning of the interval is

Assume the displayed reaction is the only chemical process and all species remain in the reacting mixture.
Which option correctly identifies the balanced stoichiometric coefficients and the final concentration of D?

20. A gaseous reaction follows

and obeys the experimentally established normalized rate law

Two experiments are performed at the same temperature with the same intrinsic rate constant.
Experiment I uses a rigid vessel of volume , initially containing moles of A and moles of B.
Experiment II uses a rigid vessel of volume , initially containing the same amounts of A and B as Experiment I.
Let and denote the initial normalized rates per unit volume.
Let and denote the corresponding initial total molar rates of reaction in each vessel.
Assume ideal-gas behaviour and homogeneous mixing.
Which pair is correct?

21. A second-order reaction

has the disappearance law

The intrinsic rate constant obeys the Arrhenius equation between and .
Two independent half-life experiments give:

Assume the rate law remains second order at both temperatures and the Arrhenius parameters are constant.
Use

Which pair gives the activation energy and the first half-life at if the initial concentration is instead ?

22. Two independent pathways consume the same reactant A:


Under the stated conditions, Pathway I follows zero-order disappearance, whereas Pathway II follows first-order disappearance.
The two pathways operate simultaneously while A remains available.
The positive instantaneous total disappearance rate is therefore

At the instant when

which pair gives the fraction of A disappearance occurring through Pathway II and the instantaneous total disappearance rate?

23. A pure gaseous reactant A undergoes the first-order decomposition

in a rigid vessel at constant temperature. Initially, the vessel contains only A at a pressure of .
After 10 min, the total pressure is .
Assume ideal-gas behaviour and first-order disappearance of A throughout the experiment.
What is the total pressure after 20 min?

24. Consider four experimentally observed kinetic situations.

Match each situation with the conclusion that necessarily follows.
List II:
(1) The overall reaction order is one.
(2) The partial order with respect to A is three.
(3) The partial order with respect to B is zero.
(4) The partial order with respect to A is one-half.
Assume ordinary power-law kinetics and a normalized reaction rate expressed in concentration per unit time.

25. The oxidation of carbon monoxide by nitrogen dioxide has the overall equation

A proposed mechanism is:
Step 1 (slow):

Step 2 (fast):

Assume that Step 1 controls the overall reaction rate and that the mechanism remains valid over the investigated concentration range.
Which experimental observation would be consistent with this mechanism?

26. A reversible elementary isomerisation

obeys separate forward and reverse Arrhenius equations with temperature-independent parameters between and .
At , the equilibrium concentration ratio is

At , the equilibrium ratio is

The forward activation energy is independently measured as

Assume

for the stated elementary reversible reaction and that the forward and reverse pathways share a consistent reaction-energy difference.
Use

Which pair gives the forward reaction-energy change and the reverse activation energy?

27. The reaction follows the rate law . Two otherwise identical experiments are performed at the same temperature, one without a catalyst and the other with a suitable catalyst.
In the uncatalysed experiment, the instantaneous concentration of A is , and its concentration–time tangent has slope .
In the catalysed experiment, the instantaneous concentration of A is , and its concentration–time tangent has slope .
Assuming the same rate-law form in both experiments, the ratio of the catalysed rate constant to the uncatalysed rate constant is:

28. A chemical transformation has an overall reaction energy change

The uncatalysed pathway has a single relevant transition-state maximum and a forward activation energy of

A catalyst introduces an alternative single-maximum pathway whose forward activation energy is lower.
The catalyst leaves the energies of the reactants and products unchanged.
Four sets of proposed activation-energy values are shown below.

Which set is fully consistent with the specified energy profile and catalytic effect?

29. Dinitrogen pentoxide decomposes according to

Its experimentally observed disappearance of is first order under the stated conditions.
The reaction occurs in a rigid vessel at constant temperature.
Initially, the partial pressure of is

and the vessel also contains an inert gas at

Neither gaseous product is present initially.
After 10 min, the total pressure is measured as

Assume ideal-gas behaviour, complete retention of all gases, and an unchanged first-order rate constant.
Which pair gives the total pressure and the partial pressure of oxygen after 20 min?

30. A reaction follows the experimentally established rate law

over the concentration range considered.
The intrinsic rate constant obeys the Arrhenius equation with temperature-independent parameters between and .
At ,

The activation energy is

Two initial-rate experiments are performed:

Use

Which pair gives the activation energy and the ratio of the measured initial rates ?

31. A reaction involving reactants A and B follows the experimentally established rate law

At a fixed temperature, Experiment I is carried out in a vessel of volume , initially containing of A and of B.
Its initial normalized reaction rate is

In Experiment II, the same initial amounts of A and B are placed in a vessel of volume . The measured total molar reaction rate is one-fourth of that in Experiment I.
In a separate initial-rate experiment at the same temperature and volume as Experiment I, doubling only the concentration of B increases the normalized rate fourfold.
Assume the same rate law and intrinsic rate constant apply throughout.
Which pair gives the partial order in A and the concentration-based rate constant?

32. A reaction follows the experimentally established second-order disappearance law

at constant temperature.

Which pair gives the rate constant and the actual instantaneous disappearance rate when

33. A first-order reaction

occurs at constant temperature and volume.
Initially,

but the initial concentration of P is unknown.
The following ratios of product concentration to remaining reactant concentration are measured:

Assume P is stable, the reaction is irreversible, and the first-order constant remains unchanged.
Which pair gives the initial concentration of P and the predicted ratio after 30 min?

34. A first-order reaction obeys the Arrhenius equation with a constant activation energy and constant pre-exponential factor.
An experimenter first constructs an Arrhenius plot using rate constants expressed in .
The experimenter then converts every measured rate constant to and constructs a second plot using the same temperature values.
Both plots have natural logarithm of the numerical rate constant on the vertical axis and on the horizontal axis.
Consider the following statements.
Statement I: Every numerical rate constant used in the second plot is 60 times its numerical value in the first plot.
Statement II: The vertical intercept of the second plot exceeds that of the first plot by .
Statement III: The slope of the second plot is 60 times the slope of the first plot.
Statement IV: Both plots give the same activation energy when interpreted using the appropriate logarithmic Arrhenius relation.
Statement V: The physical pre-exponential factor of the reaction changes merely because its numerical value is expressed in different time units.
Which combination is correct?

35. A chemical reaction can follow either an uncatalysed one-step pathway or a catalysed two-step pathway.

Which pair correctly gives the activation-energy difference between the first and second elementary steps of the catalysed forward pathway and the reduction in the overall reverse activation barrier relative to the uncatalysed pathway, respectively?

36. Two catalysts, C1 and C2, are proposed for the same chemical reaction at a fixed temperature. Both provide alternative pathways between the same initial reactants and final products.
The measured activation energy for the pathway involving C1 is lower than that for C2. However, the Arrhenius frequency factors for the two catalysed pathways are not known.
Which conclusion follows most reliably?

37. A first-order reaction obeys the Arrhenius equation with temperature-independent parameters from to .
Its measured half-lives are:

At , a fresh sample begins with

Which pair gives the activation energy and the concentration of A remaining after 5 min at ?
Use

38. A reaction

occurs in a closed constant-volume vessel. Its experimentally established normalized reaction rate is

where

Initially,

Assume the rate law remains valid while both reactants are present.
Which pair gives the concentrations of A and P after 20 min?
Use .

39. A reaction

follows first-order kinetics in a constant-volume solution at fixed temperature.
An instrument produces a numerical signal defined by

where both concentrations are expressed in , and the signal is reported on a corresponding calibrated scale.
The initial concentrations of A and P are unknown.
The measured signals are:

Assume complete eventual conversion, stable product P, unchanged volume, and no other reactions.
Which pair gives the initial concentration of P and the predicted signal after 30 min?

40. In two experiments on the same bimolecular gaseous reaction, the total A–B collision frequency and energetic fraction are held constant.
The number of effective product-forming encounters is nevertheless different.

Assume that orientation suitability is the only remaining factor controlling which energetic encounters become effective.
Which conclusion correctly gives the orientation factors and identifies what cannot be inferred from the observations?

41. A reaction proceeds through the following proposed mechanism:
Step 1 (fast):
Step 2 (slow):
Step 3 (fast):
Assume that the second step is rate-determining and that the intermediate concentration cannot be treated as independently fixed.
Consider the following statements.
Statement I: The net reaction obtained by adding all three steps is .
Statement II: I is an intermediate because it is formed and subsequently consumed.
Statement III: The molecularity of the overall complex reaction is four.
Statement IV: The rate expression of the slow elementary step contains , but the overall rate law in terms of stable reactants requires additional kinetic information.
Which combination is correct?

42. A reactant A forms two different stable products through independent parallel first-order pathways:


The total first-order disappearance constant is

Initially,

The half-life of A is 10 min.
During the first 10 min, the pathway constants satisfy

At exactly 10 min, the catalytic condition is changed instantaneously. The total first-order disappearance constant remains unchanged, but the pathway ratio becomes

The reaction continues for another 10 min.
Assume no reverse reactions, no reaction during the catalytic change, and unchanged volume.
Which pair gives the concentration of P after 20 min and its instantaneous appearance rate immediately after the catalytic change?
Use .

43. A reaction follows the experimentally established rate law

The rate constant is reported in units

At fixed temperature, Experiment II is performed using twice the A concentration and half the B concentration of Experiment I.
The measured initial rates of the two experiments are equal.
Assume the same rate law and intrinsic constant apply to both experiments.
Which option correctly gives the partial orders and predicts the rate multiplier when both reactant concentrations are doubled simultaneously?

44. A gaseous reactant A undergoes the first-order decomposition

in a rigid vessel at constant temperature.
Initially, the vessel contains A at a partial pressure of

and an inert gas at a partial pressure of

No B is initially present.
After 10 min, the measured total pressure is

At exactly 10 min, an additional quantity of inert gas is introduced instantaneously, increasing the total pressure by .
The addition does not change the vessel volume, temperature or amounts of A and B, and no reaction occurs during the addition.
The reaction subsequently continues with the same first-order rate constant.
Which pair gives the first-order rate constant and the total pressure after 30 min, measured from the original start?
Use .

45. Three candidate rate laws have been proposed for a reaction involving A and B:
Law I:
Law II:
Law III:
In an initial-rate comparison, doubling the concentrations of both A and B increases the rate fourfold. All three laws are consistent with this observation.
A second experiment is to be designed at the same temperature and within the applicable kinetic range. Which experimental change and possible observation would specifically support Law II over Laws I and III?

46. A surface-catalysed decomposition

exhibits zero-order disappearance while the concentration of A is sufficiently high.
At lower concentration, it follows first-order disappearance under the specified experimental conditions.
The kinetic behaviour is:

for

and

for

where the first-order constant has units .
Initially,

Assume both kinetic descriptions remain valid in their stated ranges and the rate is continuous at the transition.
Which pair gives the total time required for A to decrease to and the instantaneous disappearance rate at the transition?
Use .

47. A first-order reaction obeys the Arrhenius equation over the temperature range of interest.

Use

Which pair gives the activation energy and the rate constant at ?

48. A gaseous reaction proceeds according to

in a rigid vessel maintained at constant temperature. Its concentration-based normalized rate law is

At the experimental temperature,

Three initial-rate experiments are performed. The initial partial pressures and measured initial slopes of total pressure against time are:

Assume ideal-gas behaviour and the same rate constant in all experiments.
Which pair gives the concentration-based rate constant and the predicted initial slope of total pressure when and ?

49. A gaseous reaction

occurs in a rigid vessel at constant temperature. Initially, the vessel contains pure A at a pressure of . At a later instant, the measured total pressure is .
The reaction follows the experimentally established rate law , which remains valid during the observation.
Assuming ideal-gas behaviour and no competing reactions, the ratio of the instantaneous reaction rate at the later instant to its initial value is:

50. Two samples of the same reactant undergo zero-order disappearance at the same temperature, with rate constant

Sample I initially contains A at , whereas Sample II initially contains A at .
Assume zero-order behaviour remains valid until the specified target concentration is reached.
Which pair gives the times required for Samples I and II, respectively, to reach ?