1. What does the Arrhenius constant \(A\) represent?

A. Activation energy B. Frequency factor or collision frequency C. Rate constant D. Reaction order

2. What is the half-life \( t_{1/2} \) expression for a first-order reaction?

A. \( t_{1/2} = \frac{1}{k} \) B. \( t_{1/2} = \frac{0.693}{k} \) C. \( t_{1/2} = \frac{1}{k[A]_0} \) D. \( t_{1/2} = \frac{[A]_0}{2k} \)

3. Which of the following is NOT true for the collision theory of reaction rates?

A. Only collisions with sufficient energy lead to reaction. B. All collisions between reactant molecules lead to product formation. C. Orientation of molecules affects reaction probability. D. Collision frequency affects the reaction rate.

4. In kinetics, molecularity refers to:

A. The sum of exponents in the rate law B. Number of molecules colliding in an elementary step C. Power of concentration in rate law D. The frequency factor in Arrhenius equation

5. Which of these statements correctly describes molecularity?

A. It refers to how many molecules collide simultaneously in an elementary step. B. It is the sum of powers in the rate law. C. It always equals the overall reaction order. D. It is negative in an exothermic reaction.

6. Which of these will likely increase the rate constant \( k \) for a reaction?

A. Increasing activation energy \( E_a \) B. Decreasing temperature C. Increasing temperature D. Decreasing collision frequency \( A \)

7. During the evaporation of water, the enthalpy change is calculated by:

A. Subtracting the enthalpy of liquid water from water vapor. B. Adding the enthalpies of liquid and vapor states. C. Subtracting the enthalpy of water vapor from liquid water. D. Multiplying enthalpy values of both forms.

8. According to the collision theory, why do all collisions not result in a reaction?

A. Particles never collide with sufficient speed. B. Collisions occur only at constant pressure. C. Not all collisions have enough kinetic energy to break bonds and form products. D. Temperature must be below a specific threshold.

9. The relationship between the rate constant \(k\) at two different temperatures is given by the Arrhenius equation as:

A. \(\ln \frac{k_2}{k_1} = \frac{E_a}{R}\left(\frac{1}{T_1} - \frac{1}{T_2}\right)\) B. \(\ln \frac{k_2}{k_1} = -\frac{E_a}{R}\left(\frac{1}{T_1} - \frac{1}{T_2}\right)\) C. \(\frac{k_2}{k_1} = e^{-\frac{E_a}{R} (T_2 - T_1)}\) D. \(k_2 = k_1 e^{-\frac{E_a}{RT}}\)

10. The rate constant \(k\) for a first-order reaction has units of:

A. mol L\(^{-1}\) s\(^{-1}\) B. s\(^{-1}\) C. L mol\(^{-1}\) s\(^{-1}\) D. unitless

11. In the reaction \( 2NO + 2H_2 \rightarrow N_2 + 2H_2O \), if the rate law is determined experimentally as \( \text{rate} = k[NO]^2[H_2]^1 \), what is the overall order of the reaction?

A. One B. Two C. Three D. Four

12. For a reaction with rate law \( \text{rate} = k[A]^m[B]^n \), the overall order of the reaction is:

A. \( m \times n \) B. The sum \( m + n \) C. The difference \( m - n \) D. Always 2

13. How is the instantaneous rate of a reaction defined?

A. It is the average rate over a long time. B. It is the rate at the start of the reaction only. C. It is the rate at any specific instant or time during the reaction. D. It is the rate after the reaction is complete.

14. The Arrhenius equation is expressed as:

A. \(k = Ae^{E_a/RT}\) B. \(k = Ae^{-E_a/RT}\) C. \(k = Ae^{RT/E_a}\) D. \(k = Ae^{RT}\)

15. Activation energy \(E_a\) is:

A. The total energy released by a reaction B. The minimum energy required for reactant molecules to form products C. The energy of products only D. The energy difference between reactants and products

16. What is the typical order of magnitude unit of the Arrhenius constant \(A\)?

A. Same as rate constant \(k\) B. Dimensionless C. Units depend on reaction order D. Always in s\(^{-1}\)

17. If the rate constant at 25°C is \(4.5 \times 10^{-4}\) s\(^{-1}\), what happens to the rate constant at 50°C assuming constant activation energy?

A. It remains the same. B. It decreases. C. It increases. D. It becomes zero.

18. What is the order of the rate law for a reaction with rate expression \( rate = k [A]^m [B]^n \)?

A. m B. n C. \( m + n \) D. \( m \times n \)

19. A plot of \( \ln k \) versus \( 1/T \) in the Arrhenius equation yields a straight line whose slope is:

A. \( +E_a / R \) B. \( -E_a / R \) C. \( \ln A \) D. \( k \)

20. When the concentration of NO is doubled while keeping [H2] constant and the rate increases fourfold, this suggests the order with respect to NO is:

A. Zero B. One C. Two D. Half order

21. For a first-order reaction with rate constant \( k = 6.7 \times 10^{-4} \) s\(^{-1}\), what fraction of reactant remains after one half-life?

A. 75% B. 50% C. 25% D. 0%

22. In the Arrhenius plot of \(\ln k\) versus \(\frac{1}{T}\), the slope is equal to:

A. \(-\frac{E_a}{RT}\) B. \(\frac{E_a}{R}\) C. \(-\frac{E_a}{R}\) D. \(\frac{R}{E_a}\)

23. The rate law expression for a zero-order reaction is:

A. \(rate = k\) B. \(rate = k[A]\) C. \(rate = k[A]^2\) D. \(rate = k[A]^0\)

24. The enthalpy change of formation \( \Delta H_f^\circ \) of an element in its standard state at 25°C is:

A. Always positive B. Always negative C. Zero D. Depends on the element

25. In a first-order reaction, what fraction of the reactant remains after one half-life?

A. 1/4 B. 1/2 C. 3/4 D. 1/3

26. Which of the following statements is true about the order of a reaction?

A. It indicates the number of reactant molecules involved in the rate-determining step. B. It is always equal to the molecularity of the reaction. C. It is the power to which concentration of reactants are raised in the rate law. D. It can only be determined theoretically.

27. The integrated rate law for a first-order reaction is expressed as:

A. \( [A]_t = [A]_0 - kt \) B. \( \ln[A]_t = -kt + \ln[A]_0 \) C. \( 1/[A]_t = kt + 1/[A]_0 \) D. \( [A]_t^2 = [A]_0^2 - 2kt \)

28. What does a positive change in entropy (\( \Delta S > 0 \)) imply about a chemical reaction?

A. The system becomes more ordered. B. The reaction is less likely to occur. C. The system becomes more disordered, favoring spontaneity. D. The reaction is endothermic.

29. Which of the following best describes the role of activation energy in a chemical reaction?

A. It determines the total energy released by the reaction. B. It is the minimum energy needed for reactant particles to successfully collide and form products. C. It is the average kinetic energy of particles in the system. D. It measures the frequency of collisions between particles.

30. For a second-order reaction, a plot of which of the following vs. time gives a straight line?

A. \( \ln[A] \) B. \( [A] \) C. \( 1/[A] \) D. \( [A]^2 \)

31. For a first-order reaction, the integrated rate law is:

A. \(\ln[A]_t = -kt + \ln[A]_0\) B. \(\frac{1}{[A]_t} = kt + \frac{1}{[A]_0}\) C. \([A]_t = -kt + [A]_0\) D. \([A]_t = [A]_0 e^{kt}\)

32. What is the unit of the gas constant \( R \) used in the Arrhenius equation?

A. L atm mol\(^{-1}\) K\(^{-1}\) B. J mol\(^{-1}\) K\(^{-1}\) C. Cal mol\(^{-1}\) C\(^{-1}\) D. Pa mol\(^{-1}\) K\(^{-1}\)

33. What is the physical meaning of the slope in the plot of \(\ln k\) versus \(1/T\)?

A. Frequency factor \(A\) B. Activation energy divided by \(R\) with sign negative C. Rate constant \(k\) D. Temperature dependence of \(\ln k\)

34. The half-life \(t_{1/2}\) of a first-order reaction is:

A. \(\frac{0.693}{k}\) B. \(\frac{1}{k [A]_0}\) C. \(\frac{[A]_0}{2k}\) D. \(\frac{2}{k}\)

35. If the activation energy \( E_a \) for a reaction increases, what happens to the reaction rate constant \( k \) at a fixed temperature?

A. \( k \) increases B. \( k \) decreases C. \( k \) remains unchanged D. \( k \) doubles

36. In terms of collisions, a reaction only occurs if:

A. The colliding particles have zero kinetic energy B. The colliding particles have kinetic energy less than \(E_a\) C. The colliding particles have kinetic energy greater than or equal to \(E_a\) D. The colliding particles collide at any energy

37. The rate constant \( k \) for a reaction depends on temperature according to the Arrhenius equation. Which term in the equation accounts for the effect of temperature?

A. Frequency factor \( A \) B. Activation energy \( E_a \) C. Gas constant \( R \) D. Absolute temperature \( T \) in the denominator of the exponential term

38. The Arrhenius constant \( A \) in the Arrhenius equation represents:

A. The activation energy of the reaction. B. The frequency of collisions and their proper orientation. C. The rate constant at infinite temperature. D. The energy of products minus reactants.

39. Which of the following best describes an activated complex?

A. The products after reaction completion B. The intermediate species at the peak of the activation energy barrier C. The reactants before collision D. The stable intermediates in the mechanism

40. The rate law of the reaction \(2NO + 2H_2 \to N_2 + 2H_2O\) is determined experimentally as:

A. \(rate = k[NO][H_2]\) B. \(rate = k[NO]^2[H_2]^2\) C. \(rate = k[NO]^2[H_2]\) D. The rate law must be determined experimentally

41. What is the unit of the gas constant \(R\) used in the Arrhenius equation?

A. J mol\(^{-1}\) K B. J mol\(^{-1}\) K\(^{-1}\) C. kJ mol\(^{-1}\) K\(^{-1}\) D. kJ mol\(^{-1}\)

42. In the rate law determination experiment with changes in reactant concentrations, if doubling the concentration of \( [B] \) does not change the rate, then the order with respect to \( B \) is:

A. Zero B. One C. Two D. Negative one

43. How does the rate of reaction relate to the collision frequency for gas-phase reactions?

A. Rate equals collision frequency B. Rate decreases as collision frequency increases C. Rate is proportional to collision frequency D. Rate is independent of collision frequency

44. Which of the following graphs would yield a straight line for a second-order reaction?

A. \(\ln [A]\) vs time B. \(1/[A]\) vs time C. \([A]\) vs time D. \(\ln k\) vs \(1/T\)

45. For a first-order reaction, if the rate constant \(k = 4.5 \times 10^{-4}\) s\(^{-1}\) at 25°C, what effect does increasing the temperature to 50°C generally have on \(k\)?

A. \(k\) remains the same B. \(k\) decreases C. \(k\) increases D. \(k\) becomes zero

46. The average rate of a reaction is defined as:

A. Instantaneous rate at time t B. Change in concentration over change in time C. Rate of disappearance of product D. Time taken for completion of reaction

47. The units of a first-order rate constant \(k\) are:

A. s\(^{-1}\) B. mol L\(^{-1}\) s\(^{-1}\) C. L mol\(^{-1}\) s\(^{-1}\) D. mol\(^{-1}\) L s\(^{-1}\)

48. Which of the following statements about the activation energy \(E_a\) is FALSE?

A. \(E_a\) is always positive B. \(E_a\) represents the energy barrier to the reaction C. Increasing temperature decreases \(E_a\) D. If collision energy is less than \(E_a\), reaction is unlikely

49. The mathematical expression for the instantaneous rate of a first-order reaction is:

A. \(rate = -\frac{d[A]}{dt} = k[A]\) B. \(rate = \frac{d[A]}{dt} = k[A]^2\) C. \(rate = \frac{d[A]}{dt} = k\) D. \(rate = -\frac{d[A]}{dt} = k\)

50. In a zero-order reaction, how does the concentration of reactant \( [A] \) change over time?

A. Exponentially decreases. B. Linearly decreases. C. Increases linearly. D. Remains constant.