1. Which statement best defines the reaction rate?
- (A) Change in temperature per unit time
- (B) Change in concentration per unit time
- (C) Change in pressure per unit time
- (D) Change in volume per unit time
View Answer
2. What is the SI-style unit for reaction rate?
- (A) s
- (B) M
- (C) M·s\(^{-1}\)
- (D) s\(^{-1}\)
View Answer
3. According to collision theory, a successful reaction requires:
- (A) Frequent collisions only
- (B) Proper orientation only
- (C) Collisions with energy ≥ \(E_a\) only
- (D) Collision + proper orientation + energy ≥ \(E_a\)
View Answer
4. Which change increases collision frequency most directly for gases?
- (A) Decreasing pressure
- (B) Increasing volume
- (C) Increasing pressure (or concentration)
- (D) Adding an inert solid
View Answer
5. Temperature increases rate because:
- (A) It lowers the activation energy \(E_a\)
- (B) It increases the fraction of molecules with \(E \ge E_a\)
- (C) It changes stoichiometric coefficients
- (D) It creates new intermediates
View Answer
6. A catalyst typically:
- (A) Increases \(E_a\) and decreases \(k\)
- (B) Lowers \(E_a\) and increases \(k\)
- (C) Changes \(\Delta H_{\text{rxn}}\)
- (D) Is consumed stoichiometrically
View Answer
7. For \(m\text{A} + n\text{B} \to \text{products}\), a general rate law is:
- (A) \(\text{Rate}=k[\text{A}]^m[\text{B}]^n\) (orders must be coefficients)
- (B) \(\text{Rate}=k[\text{A}]^x[\text{B}]^y\) (orders are determined experimentally)
- (C) \(\text{Rate}=k\) only
- (D) \(\text{Rate}=k[\text{A}][\text{B}]/t\)
View Answer
8. If doubling \([\text{A}]\) (with \([\text{B}]\) constant) doubles the rate, the order in A is:
- (A) 0
- (B) 1
- (C) 2
- (D) 1/2
View Answer
9. If doubling \([\text{A}]\) (with \([\text{B}]\) constant) increases the rate by a factor of 4, the order in A is:
- (A) 0
- (B) 1
- (C) 2
- (D) 3
View Answer
10. The units of \(k\) for a zero-order reaction are most likely:
- (A) M·s\(^{-1}\)
- (B) s\(^{-1}\)
- (C) M\(^{-1}\)·s\(^{-1}\)
- (D) M\(^{1-n}\)·s\(^{-1}\) with \(n=0\)
View Answer
11. The units of \(k\) for a first-order reaction are:
- (A) M·s\(^{-1}\)
- (B) s\(^{-1}\)
- (C) M\(^{-1}\)·s\(^{-1}\)
- (D) M\(^{-2}\)·s\(^{-1}\)
View Answer
12. The units of \(k\) for a second-order reaction (overall) are:
- (A) s\(^{-1}\)
- (B) M·s\(^{-1}\)
- (C) M\(^{-1}\)·s\(^{-1}\)
- (D) M\(^{-2}\)·s\(^{-1}\)
View Answer
13. Which plot is linear for a zero-order reaction?
- (A) \([\text{A}]\) vs \(t\)
- (B) \(\ln[\text{A}]\) vs \(t\)
- (C) \(1/[\text{A}]\) vs \(t\)
- (D) \(\ln k\) vs \(1/T\)
View Answer
14. Which plot is linear for a first-order reaction?
- (A) \([\text{A}]\) vs \(t\)
- (B) \(\ln[\text{A}]\) vs \(t\)
- (C) \(1/[\text{A}]\) vs \(t\)
- (D) \([\text{A}]^{1/2}\) vs \(t\)
View Answer
15. Which plot is linear for a second-order reaction (in A only)?
- (A) \([\text{A}]\) vs \(t\)
- (B) \(\ln[\text{A}]\) vs \(t\)
- (C) \(1/[\text{A}]\) vs \(t\)
- (D) \([\text{A}]^{2}\) vs \(t\)
View Answer
16. Which statement about half-life is TRUE?
- (A) Zero-order: \(t_{1/2}=\frac{0.693}{k}\)
- (B) First-order: \(t_{1/2}\) is constant and equals \(\frac{0.693}{k}\)
- (C) Second-order: \(t_{1/2}\) is independent of \([\text{A}]_0\)
- (D) All orders have constant \(t_{1/2}\)
View Answer
17. If the measured half-life does not depend on initial concentration, the reaction is most likely:
- (A) Zero-order
- (B) First-order
- (C) Second-order
- (D) Third-order
View Answer
18. A plot of ln[A] vs. t for a reaction is linear with slope -0.250 s⁻¹. What is the half-life?
- (A) 1.39 s
- (B) 2.77 s
- (C) 3.47 s
- (D) 4.00 s
View Answer
19. At constant temperature, which change most directly increases reaction rate by raising collision frequency rather than changing the energy distribution?
- (A) Increasing temperature
- (B) Increasing pressure of gaseous reactants
- (C) Adding an inert solvent at the same concentrations
- (D) Decreasing surface area of a solid reactant
View Answer
20. Which change directly alters the rate constant \(k\)?
- (A) Changing concentration
- (B) Changing surface area
- (C) Changing temperature
- (D) Diluting with solvent but same \(T\)
View Answer
21. Consider the mechanism:
Step 1: \(2\text{A} + \text{B} \rightleftharpoons \text{C}\) (fast, reversible)
Step 2: \(\text{C} + \text{E} \to \text{D} + \text{A}\) (slow, R.D.S)
- (A) Intermediate: A
- (B) Intermediate: C
- (C) Catalyst: C
- (D) Catalyst: E
View Answer
22. In the mechanism above, which species acts as a catalyst?
- (A) A
- (B) B
- (C) C
- (D) E
View Answer
23. Using the given mechanism (Step 2 slow), the experimental rate law is most consistent with:
- (A) \(\text{Rate}=k[\text{A}]^2[\text{B}][\text{E}]\)
- (B) \(\text{Rate}=k[\text{C}][\text{E}]\)
- (C) \(\text{Rate}=k[\text{A}]^2[\text{B}]\)
- (D) \(\text{Rate}=k[\text{E}]^2\)
View Answer
24. If Step 1 were the slow step instead, the expected rate law would most likely be:
- (A) \(\text{Rate}=k[\text{A}]^2[\text{B}]\)
- (B) \(\text{Rate}=k[\text{A}]^2[\text{B}][\text{E}]\)
- (C) \(\text{Rate}=k[\text{C}][\text{E}]\)
- (D) \(\text{Rate}=k[\text{E}]\)
View Answer
25. For \(\text{Rate}=k[\text{A}]^2[\text{B}][\text{E}]\), the overall reaction order is:
- (A) 2
- (B) 3
- (C) 4
- (D) Not defined
View Answer
26. Which statement is TRUE regarding \(\Delta H_{\text{rxn}}\) when a catalyst is added?
- (A) \(\Delta H_{\text{rxn}}\) decreases
- (B) \(\Delta H_{\text{rxn}}\) increases
- (C) \(\Delta H_{\text{rxn}}\) is unchanged
- (D) \(\Delta H_{\text{rxn}}\) becomes zero
View Answer
27. At constant temperature, increasing volume of a gas-phase mixture generally:
- (A) Increases rate for positive-order reactions
- (B) Decreases rate for positive-order reactions
- (C) Has no effect on rate
- (D) Always doubles the rate
View Answer
28. Which of the following does not change the numerical value of \(k\) at a fixed mechanism?
- (A) Changing concentration
- (B) Changing temperature
- (C) Adding a catalyst
- (D) Replacing catalyst with a different one
View Answer
29. You test order by plotting \([\text{A}], \ln[\text{A}], 1/[\text{A}]\) vs \(t\). The only linear plot is \(\ln[\text{A}] \) vs \(t\). Conclude that the reaction is:
- (A) Zero-order in A
- (B) First-order in A
- (C) Second-order in A
- (D) Third-order in A
View Answer
30. A reaction follows Rate = k[A]²[B][E]. If [B] and [E] are kept in large excess so they remain effectively constant, what is the apparent overall order and which plot is linear?
- (A) First-order overall;
ln[A]vstlinear - (B) Second-order in A (apparent overall third-order constant folded into k);
1/[A]vstlinear - (C) Zero-order overall;
[A]vstlinear - (D) Third-order overall;
1/[A]vstlinear with slope k
View Answer
[B] and [E] constant, Rate = k' [A]² where k' = k[B][E]. The kinetics appear second-order in A (pseudo-conditions), so 1/[A] vs t is linear. Reference formulas
- Rate law:
Rate = k · [A]^m · [B]^n(orders by experiment) - Integrated: Zero \([\text{A}]= -kt + [\text{A}]_0\); First \(\ln[\text{A}]= -kt + \ln[\text{A}]_0\); Second \(1/[\text{A}] = kt + 1/[\text{A}]_0\)
- Half-life: First \(t_{1/2}=0.693/k\); Zero \(t_{1/2}=[\text{A}]_0/(2k)\); Second \(t_{1/2}=1/(k[\text{A}]_0)\)
- Arrhenius: \(\ln k = \ln A - E_a/(RT)\)
- Mechanism example (given): Step 1 fast \(2\text{A}+\text{B}\rightleftharpoons \text{C}\); Step 2 slow \(\text{C}+\text{E}\to\text{D}+\text{A}\) ⇒ \(\text{Rate}\propto [\text{A}]^2[\text{B}][\text{E}]\)
31. From the initial-rates data (Rate in M·s\(^{-1}\)):
Exp 1: [A]=0.10, [B]=0.10 → Rate=0.20
Exp 2: [A]=0.20, [B]=0.10 → Rate=0.80
Exp 3: [A]=0.10, [B]=0.20 → Rate=0.40
For \(\text{Rate}=k[\text{A}]^m[\text{B}]^n\), what are \(m,n\)?
- (A) \(m=1, n=1\)
- (B) \(m=2, n=1\)
- (C) \(m=1, n=2\)
- (D) \(m=2, n=2\)
View Answer
32. Using the data in Q31 and \(\text{Rate}=k[\text{A}]^2[\text{B}]\), what is \(k\) (assume rate in M·s\(^{-1}\))?
- (A) \(20\ \text{M}^{-2}\text{s}^{-1}\)
- (B) \(200\ \text{M}^{-2}\text{s}^{-1}\)
- (C) \(2.0\ \text{M}^{-2}\text{s}^{-1}\)
- (D) \(0.20\ \text{M}^{-2}\text{s}^{-1}\)
View Answer
33. Pseudo-first-order conditions for \(\text{Rate}=k[\text{A}]^m[\text{B}]^n\) are achieved by:
- (A) Keeping both [A] and [B] very small
- (B) Keeping [A] \(\gg\) [B] constant and measuring B
- (C) Keeping [B] \(\gg\) [A] constant and measuring A
- (D) Varying both [A] and [B] simultaneously
View Answer
34. The instantaneous rate at time \(t\) is best obtained from:
- (A) Slope of a secant over a large time interval
- (B) Slope of the tangent to \([\text{A}]\) vs \(t\) at time \(t\)
- (C) Final minus initial concentration
- (D) Half of the average rate
View Answer
35. Which is TRUE regarding intermediates and transition states (TS)?
- (A) TS are local minima; intermediates are maxima
- (B) Intermediates are local minima; TS are maxima on energy profile
- (C) Both can be isolated routinely
- (D) Neither affects the rate law
View Answer
36. The elementary step \(\text{A} + 2\text{B} \to \text{C}\) is:
- (A) Unimolecular
- (B) Bimolecular
- (C) Termolecular
- (D) Zeromolecular
View Answer
37. Which slow (rate-determining) step is consistent with \(\text{Rate}=k[\text{A}]^2[\text{B}]\)?
- (A) \(2\text{A}+\text{B}\to \text{C}\)
- (B) \(\text{A}+\text{B}\to \text{C}\)
- (C) \(\text{A}\to \text{C}\)
- (D) \(\text{B}\to \text{C}\)
View Answer
38. For a first-order reaction with \(k=0.231\ \text{s}^{-1}\), the half-life \(t_{1/2}\) is:
- (A) 1.50 s
- (B) 3.00 s
- (C) 6.00 s
- (D) 0.693 s
View Answer
39. Zero-order: \(k=0.050\ \text{M·s}^{-1}\), \([\text{A}]_0=1.00\ \text{M}\). Time to reach \([\text{A}]=0.25\ \text{M}\)?
- (A) 5.0 s
- (B) 10 s
- (C) 15 s
- (D) 20 s
View Answer
40. Second-order in A: \(k=0.200\ \text{M}^{-1}\text{s}^{-1}\), \([\text{A}]_0=0.500\ \text{M}\). \(t_{1/2}\) is:
- (A) 2.0 s
- (B) 5.0 s
- (C) 10 s
- (D) 20 s
View Answer
41. At a fixed temperature, adding a catalyst will:
- (A) Change the equilibrium constant \(K\)
- (B) Change \(\Delta H^\circ\)
- (C) Speed up both forward and reverse reactions equally, leaving \(K\) unchanged
- (D) Stop the reverse reaction
View Answer
42. A three-step mechanism has activation energies: Step 1 = 10 kJ·mol\(^{-1}\), Step 2 = 25 kJ·mol\(^{-1}\), Step 3 = 5 kJ·mol\(^{-1}\). The RDS is:
- (A) Step 1
- (B) Step 2
- (C) Step 3
- (D) None (all equal)
View Answer
43. Which best increases the orientation factor in collisions?
- (A) Using an enzyme active site that binds substrates in a specific geometry
- (B) Increasing solvent viscosity
- (C) Decreasing temperature
- (D) Using an inert diluent gas
View Answer
44. For a plot of \(\ln k\) vs \(1/T\), the slope is \(-1.20\times10^4\ \text{K}\). The activation energy \(E_a\) is approximately:
- (A) 12.0 kJ·mol\(^{-1}\)
- (B) 50.0 kJ·mol\(^{-1}\)
- (C) 100 kJ·mol\(^{-1}\)
- (D) 1,200 kJ·mol\(^{-1}\)
View Answer
45. Overall: \(\text{A}+2\text{B}\to \text{products}\). Measured: \(\text{Rate}=k[\text{A}][\text{B}]\). Which explanation fits?
- (A) The slow step involves \(\text{A}+\text{B}\); the second B reacts in a fast step
- (B) The slow step is unimolecular in A only
- (C) The reaction is zero order overall
- (D) Orders must equal stoichiometric coefficients
View Answer
46. The units of \(k\) for an overall fourth-order reaction are:
- (A) \(\text{s}^{-1}\)
- (B) \(\text{M}^{-1}\text{s}^{-1}\)
- (C) \(\text{M}^{-2}\text{s}^{-1}\)
- (D) \(\text{M}^{-3}\text{s}^{-1}\)
View Answer
47. If all reactant concentrations are halved in a third-order reaction overall, the rate becomes:
- (A) Unchanged
- (B) Half
- (C) One-quarter
- (D) One-eighth
View Answer
48. For \(\text{Rate}=k[\text{A}]^0[\text{B}]^1\), doubling [A] while keeping [B] constant will:
- (A) Double the rate
- (B) Halve the rate
- (C) Not change the rate
- (D) Quadruple the rate
View Answer
49. For \(2\text{A}\to \text{P}\), which relation is correct?
- (A) \(\text{Rate}=\dfrac{d[\text{A}]}{dt}\)
- (B) \(\dfrac{d[\text{P}]}{dt}=-\dfrac{d[\text{A}]}{dt}\)
- (C) \(\dfrac{d[\text{P}]}{dt}=-\dfrac{1}{2}\dfrac{d[\text{A}]}{dt}\)
- (D) \(\dfrac{d[\text{P}]}{dt}=-2\dfrac{d[\text{A}]}{dt}\)
View Answer
50. If \(k\) has units \(\text{M}^{-2}\text{s}^{-1}\), the overall reaction order is:
- (A) 1
- (B) 2
- (C) 3
- (D) 4
View Answer
51. Why don’t experimental rate-law orders necessarily match the coefficients of the overall balanced equation?
- (A) Measurement error
- (B) Orders are always integers
- (C) Overall reaction sums multiple elementary steps; RDS dictates observed orders
- (D) Because rate is independent of mechanism
View Answer
52. Zero-order with \(k=2.0\times10^{-3}\ \text{M·s}^{-1}\) and \([\text{A}]_0=0.100\ \text{M}\). Time until \([\text{A}]=0\)?
- (A) 25 s
- (B) 40 s
- (C) 50 s
- (D) 100 s
View Answer
53. First-order with \(k=0.100\ \text{min}^{-1}\), \([\text{A}]_0=0.800\ \text{M}\). Time to reach \([\text{A}]=0.100\ \text{M}\)?
- (A) 6.93 min
- (B) 13.9 min
- (C) 20.8 min
- (D) 27.7 min
View Answer
54. Second-order in A: \([\text{A}]_0=0.400\ \text{M}\), after 25.0 s \([\text{A}]=0.200\ \text{M}\). Find \(k\).
- (A) \(0.050\ \text{M}^{-1}\text{s}^{-1}\)
- (B) \(0.075\ \text{M}^{-1}\text{s}^{-1}\)
- (C) \(0.100\ \text{M}^{-1}\text{s}^{-1}\)
- (D) \(0.200\ \text{M}^{-1}\text{s}^{-1}\)
View Answer
55. Which experiment most directly indicates first-order behavior?
- (A) \([\text{A}]\) vs \(t\) is linear
- (B) \(1/[\text{A}]\) vs \(t\) is linear
- (C) \(\ln[\text{A}]\) vs \(t\) is linear with slope \(-k\)
- (D) Rate independent of [A]
View Answer
56. The method of isolation (flooding) is used to:
- (A) Determine activation energy
- (B) Determine the order with respect to a single reactant by holding others in large excess
- (C) Balance redox equations
- (D) Measure equilibrium constants only
View Answer
57. Which statement about reaction orders is TRUE?
- (A) They must be positive integers
- (B) They equal stoichiometric coefficients
- (C) They can be zero, fractional, or even negative and are determined experimentally
- (D) They are independent of the mechanism
View Answer
58. Finely dividing a solid reactant typically:
- (A) Decreases rate by reducing collisions
- (B) Increases rate by increasing available surface sites
- (C) Makes rate zero
- (D) Only changes equilibrium position
View Answer
59. A two-step mechanism has how many transition states and intermediates?
- (A) 1 TS and 0 intermediates
- (B) 2 TS and 1 intermediate
- (C) 2 TS and 2 intermediates
- (D) 1 TS and 1 intermediate
View Answer
60. Which statement about catalysts in rate laws is MOST accurate?
- (A) Catalysts never appear in rate laws
- (B) Catalysts always appear squared in rate laws
- (C) A catalyst can appear in the rate law if it participates in or affects the RDS/pre-equilibrium
- (D) Catalysts only change \(\Delta H\), not \(E_a\) or \(k\)