Chemical Kinetics Mock Test – Class 12 Chemistry

1. A vessel initially contains gaseous and an inert gas at a total pressure of . The reaction is first order. The final total pressure is , and after the pressure is . The rate constant is:

2. A reaction has and . The enthalpy change for the forward reaction is:

3. An uncatalysed reaction has and . A catalyst lowers the forward activation energy to . For the same overall reaction, the catalysed reverse activation energy is:

4. Assertion: A single concentration measurement at one non-zero time is usually insufficient to establish reaction order.
Reason: Different integrated rate laws can often be fitted to one initial and one later concentration by choosing different values of .

5. A catalyst is introduced into a reversible reaction at fixed temperature. It lowers the activation energies of both the forward and reverse pathways. Which change is expected?

6. Because continuous instrumental monitoring is impractical for a slow reaction, small portions are withdrawn at regular times, rapidly cooled, and titrated to determine the amount of reactant remaining. Rapid cooling before titration is mainly intended to:

7. In the rate law , the rate constant is:

8. Which feature may appear on a catalysed energy profile even when the uncatalysed profile has only one peak?

9. The progress of a reaction is monitored through the concentration of reactant . The average disappearance rates over successively shorter intervals around are shown below.

The best estimate of the instantaneous disappearance rate at is:

10. For a zero-order reaction, a graph of against is a straight line whose:

11. A reaction obeys . Which unit belongs to ?

12. The collision-theory parameters are , , and . The predicted rate constant is:

13. The slowest step in a simple consecutive mechanism is often compared with a narrow section of a pipeline because:

14. Two straight lines are obtained on plots of against . Line P has slope , while Line Q has slope . Which conclusion is correct?

15. The initial concentration of a first-order reactant is and . The concentration after is closest to:

16. Assertion: During the decomposition at constant temperature and volume, the total pressure increases even though the partial pressure of decreases.
Reason: Each mole of consumed produces two moles of gaseous products.

17. The reaction between and is studied at constant temperature. Doubling while keeping fixed doubles the initial rate. Doubling while keeping fixed quadruples the initial rate. The supported differential rate law is:

18. Assertion: Amounts may replace concentrations in a first-order integrated equation when the volume is constant.
Reason: The ratio of initial to remaining amount is then equal to the corresponding concentration ratio.

19. Assertion: A catalyst does not alter the equilibrium constant of a reversible reaction at fixed temperature.
Reason: It accelerates the forward and reverse reactions by providing lower-barrier pathways for both directions.

20. Chemical kinetics is primarily concerned with:

21. On a graph with concentration on the vertical axis and time on the horizontal axis, the slope between two points represents:

22. The rate constant of a reaction has the same unit as the reaction rate. The overall order of the reaction is:

23. A photochemical reaction is zero order in reactant while the absorbed light intensity remains constant. If the absorbed photon flux is doubled without changing other conditions, the rate is expected to:

24. A normalised molecular-energy distribution curve has molecular energy on the horizontal axis and a total area of . A vertical line marks the activation energy . The area beneath the curve to the right of this line represents:

25. Assertion: The integrated first-order rate equation contains a logarithm of concentration.
Reason: Integration of gives .

26. A reaction proceeds through three elementary steps and contains two detectable intermediates. Why can a single-collision description be inadequate?

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

28. Assertion: The slope of an Arrhenius plot of against is negative, although activation energy is positive.
Reason: The slope is equal to .

29. Consider the following statements about molecular-energy distributions.
Statement I: At any non-zero temperature, molecules do not all possess the same kinetic energy.
Statement II: Increasing temperature increases the area under the normalised curve.
Statement III: Increasing temperature increases the fraction of molecules with energy above a fixed .
The valid statements are:

30. The concentration of a product increases from to in . Its average rate of appearance in is:

31. Two experiments use identical initial concentrations and the same catalyst condition, but Experiment Q is performed at a higher temperature than Experiment P. If the reaction mechanism remains unchanged, the most likely result is:

32. Two mixtures contain the same reactants in the same proportions but are maintained at different temperatures. Their reaction speeds:

33. Complete the missing species so that it behaves as an intermediate.

34. Absorbance, which is proportional to reactant concentration, is used to monitor a first-order reaction.

The predicted absorbance at is closest to:

35. Initial-rate observations for a reaction involving and are summarised below.

The supported rate law is:

36. A differential rate equation and an integrated rate equation differ mainly because:

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

38. In at constant temperature and volume, match each quantity in Column I with the expression in Column II.

39. Rate constants calculated from the same concentration-time data using zero-order and first-order equations are shown below.

The data most strongly support:

40. The common-logarithm form of the first-order rate equation is obtained using:

41. Consider the following statements for a zero-order reaction at fixed temperature.
Statement I: is directly proportional to .
Statement II: is inversely proportional to .
Statement III: Every successive halving of the remaining concentration requires the same time.
The valid statements are:

42. Two zero-order experiments are conducted at the same temperature with the same rate constant. Experiment P begins at , while Experiment Q begins at . Their -against- graphs will:

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

44. A secant and a tangent are drawn on the same curved reactant concentration-time graph. Their kinetic meanings are:

45. The common-logarithm form of the Arrhenius equation is:

46. For first-order decomposition

starting with pure at pressure , the appropriate pressure-based rate equation is:

47. Assertion: For the reaction , the numerical decrease in need not equal the numerical increase in .
Reason: The concentration changes of and are related through their stoichiometric coefficients.

48. Assertion: A reaction can proceed faster at a higher temperature even when the reactant concentrations are initially the same.
Reason: The rate constant of the reaction commonly increases with temperature.

49. 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:

50. Pressure-method statements for first-order kinetics are listed below.
Statement I: Temperature and volume should remain constant during the measurements.
Statement II: The measured total pressure can always be used directly as the remaining reactant pressure.
Statement III: The final pressure helps convert total-pressure data into the partial pressure of unreacted gas.
The valid statements are: