Chemical Kinetics Mock Test – Class 12 Chemistry

1. The fraction of collisions having sufficient energy to cross an activation barrier is commonly represented in simple collision theory by:

2. A linear zero-order concentration-time graph has vertical intercept and slope . The extrapolated time-axis intercept is:

3. Under the rate law , is reduced to one-half of its original value at fixed temperature and catalyst condition. Which change occurs immediately?

4. A pseudo-first-order experiment gives a straight line when is plotted against time. The slope of this line is:

5. Assertion: Initial-rate experiments should be performed at the same temperature when concentration effects are being compared.
Reason: A temperature change can alter the rate constant and obscure the concentration dependence.

6. Two zero-order reactions P and Q have the same half-life. Their initial concentrations satisfy . The ratio of their rate constants is:

7. For reaction , the instantaneous rate of appearance of is . The instantaneous rate of disappearance of is:

8. A proposed rate law is used to calculate from four independent initial-rate experiments. The values obtained are shown below.

All experiments were performed at the same temperature and catalyst condition. The most suitable conclusion is:

9. The overall equation is , but experiment gives . Which conclusion is most appropriate?

10. Increasing the concentration of a reactant often increases the reaction rate because:

11. For the elementary step

the rate law is most reasonably written as:

12. Assertion: A catalyst does not change the enthalpy change of a reaction.
Reason: It lowers the energy of the transition-state pathway without changing the energy difference between reactants and products.

13. For a forward reaction monitored from its initial mixture, the usual concentration trends are:

14. A product concentration-time curve has a horizontal tangent at a particular instant. At that instant:

15. Use the arrangement described below. A conical flask containing a reaction mixture is placed on a balance. The flask is loosely plugged with cotton so that a gaseous product can escape while liquid droplets are retained. The balance reading is recorded at regular times. The observed mass decrease is most directly related to:

16. The first-order rate constant is . The time required for only of the reactant to remain is closest to:

17. A student argues that the reactions and must have rate laws and , respectively. The argument is valid only when:

18. Reactant changes from concentration at to at , where . Its average rate of disappearance is:

19. The collision-theory expression for a rate constant is commonly written as:

20. Three proposed methods for diagnosing reaction order are listed below.
Statement I: Testing whether the appropriate integrated plot is linear.
Statement II: Checking whether calculated values of remain approximately constant.
Statement III: Copying reactant coefficients from the balanced overall equation.
The valid methods are:

21. The instantaneous rate of a reaction at time is obtained conceptually by:

22. Assertion: Reaction order may change when the reaction conditions or dominant mechanism change.
Reason: Molecularity of a specified elementary step can take fractional values under different conditions.

23. For ideal gaseous reactants, evaluate the effects described below.
Statement I: At fixed temperature, the partial pressure of a gas is proportional to its molar concentration.
Statement II: The rate response to pressure depends on the powers of gaseous-reactant terms in the rate law.
Statement III: Doubling every reactant partial pressure does not always merely double the rate.
The valid statements are:

24. The concentration of reactant was measured at several times.

If , , and are the average disappearance rates over , , and , respectively, their order is:

25. Which role of a balanced chemical equation is most relevant as a prerequisite for studying reaction rates?

26. Assertion: The expression

can remain valid when an inert gas is initially present.
Reason: The constant inert-gas pressure cancels when the pressure differences are formed.

27. Consider the following statements about basic kinetic notation.
Statement I: commonly represents time.
Statement II: commonly represents reactant concentration.
Statement III: commonly represents the rate constant.
The valid statements are:

28. Which statement best describes reaction order?

29. A reversible reaction is allowed to proceed in two identical closed vessels at the same temperature. A catalyst is added only to Vessel P. Compared with Vessel Q, Vessel P will:

30. Assertion: Collision theory is more successful qualitatively than quantitatively for many complex reactions.
Reason: Real molecules may have complicated energy redistribution, intermolecular forces, and multistep pathways.

31. When doubling increases the reaction rate by a factor of , the order with respect to is ______.

32. Consider the following statements about pseudo-first-order kinetics.
Statement I: The observed first-order constant may depend on the concentration of the excess reactant.
Statement II: The true overall reaction order necessarily becomes one.
Statement III: The excess reactant must change negligibly during the measured interval.
The valid statements are:

33. Absorbance readings for a coloured reactant are shown below. Under the measurement conditions, absorbance is directly proportional to its concentration.

The data indicate that:

34. Activation energy is described through the following statements.
Statement I: It represents an energy barrier that reacting species must overcome.
Statement II: It is necessarily equal to the enthalpy change of reaction.
Statement III: It is commonly expressed in .
The valid statements are:

35. Zero-order disappearance begins with of a reactant and has . The idealised completion time is:

36. A catalyst lowers the activation energy from to . Assuming the same pre-exponential factor, the ratio at is closest to:

37. Dividing a species-based rate by its stoichiometric coefficient is necessary because:

38. When common logarithms are used, a plot of against for a first-order reaction has slope:

39. The units of rate constants are assessed through the statements below.
Statement I: The time dimension of is always reciprocal time for a rate law written in the usual concentration form.
Statement II: The concentration dimension of depends on the overall reaction order.
Statement III: The unit of reaction rate changes with reaction order.
The valid statements are:

40. A first-order reactant and its product both absorb strongly at the wavelength used by a colorimeter. Why is the total absorbance not automatically suitable for direct substitution in the first-order equation?

41. At temperature , of molecules have energy at least equal to . At a higher temperature , this fraction becomes . If collision frequency and orientation factor are assumed unchanged, the energetic contribution to the rate increases by a factor of:

42. Concentration-time data for a reaction are shown below.

If the reaction is zero order, the graph parameters are:

43. A measurable property can be used to monitor a reaction rate only when:

44. An inert gas is added to a gaseous reaction at constant temperature while the total pressure is kept constant by allowing the vessel to expand. What may happen to the reaction rate if the rate law has positive orders in the gaseous reactants?

45. Evaluate the three statements about stoichiometrically normalised rate.
Statement I: Such normalised rate expressions are commonly applied under constant-volume conditions.
Statement II: At constant volume, concentration changes are directly proportional to changes in molar amounts.
Statement III: If volume changes substantially, concentration may change for reasons other than chemical consumption or formation.
The valid statements are:

46. For the constant-volume reaction , the tangent slope of the -versus- curve at a selected instant is . At the same instant, the tangent slope of the -versus- curve is:

47. The rate law is . If is doubled while is reduced to one-half of its original value at constant temperature, the new rate is:

48. A reactant concentration falls from to during the first . It then falls from to during the next . The data show that:

49. On a straight-line Arrhenius plot of against , the point corresponding to the higher temperature lies:

50. Use the energy-profile description below. Path P and Path Q connect the same reactant-energy level to the same product-energy level. Path P has a much higher maximum than Path Q. If Path Q represents the catalysed route, the supported conclusion is: