5 STEPS TO A 5: 500 AP Chemistry Questions to Know by Test Day! (2012)

Questions 270–273 refer to the following choices:

(A) Rate = k [M]

(B) Rate = k [M][N]

(C) Rate = k [M][N]²

(D) Rate = k [M]²[N]²

(E) Rate = k [N]²

270. Doubling the concentration of M has no effect on the reaction rate.

271. Doubling the concentration of M and N increases reaction rate by 2.

272. Doubling the concentration of M only quadruples the reaction rate.

273. Doubling the concentration of M and N increases the reaction rate by eight fold. Halving the concentration of N decreases the reaction rate four fold.

274. The production of iron (II) sulfide occurs at a significantly higher rate when iron filings are used instead of blocks (volume = 0.1 mL). Which of the following best explains this observation?

(A) The iron filings are partially oxidized due to their greater exposure to oxygen.

(B) The iron in the block is Fe_(s) and the iron in the filings is Fe²⁺.

(C) The iron block is too concentrated to chemically react.

(D) The iron filings have a much greater area in contact with sulfur.

(E) The reactant order of iron in the rate law is 1 for Fe_(s) and 2 for Fe²⁺.

275. A chemistry student sitting around a campfire observes that the large pieces of wood burn slowly, but a mixture of small scraps of wood and sawdust added to the flame combusts explosively. The correct explanation for the difference in the combustion between these two forms of wood is that, compared with the wood scraps and sawdust, the large pieces of wood

(A) have a greater surface area-to-volume ratio.

(B) have a smaller surface area per kilogram.

(C) have a higher percent carbon.

(D) contain compounds with a lower heat of combustion.

(E) contain more carbon dioxide and water.

276. All of the following result in an increased rate of reaction in an aqueous solution except:

(A) Increasing the temperature of an endothermic reaction.

(B) Increasing the temperature of an exothermic reaction.

(C) Increasing the surface area of a solid reactant.

(D) Increasing the pressure on the solution.

(E) Mixing or stirring the solution.

277. Factors that affect the rate at which a chemical reaction proceeds include which of the following?

I. The orientation of the reactants at time of collision

II. The kinetic energy of the collisions between reactants

III. The frequency of collisions between reactants

(A) I only

(B) II only

(C) III only

(D) I and II only

(E) I, II, and III

278. Which of the following correctly explain(s) the effect of increased temperature on the rate of a chemical reaction?

I. Increases the reaction rate of endothermic reactions

II. Increases the reaction rate of exothermic reactions

III. Decreases the reaction rate of reactions with a –ΔH

(A) I only

(B) II only

(C) I and II only

(D) II and III only

(E) I and III only

279. All of the following statements regarding the kinetics of radioactive decay are true except:

(A) The length of time of a half-life is specific to a particular element.

(B) All radioactive decay displays first-order kinetics.

(C) In a sample of a pure, radioactive isotope, one-half the number of radioactive atoms and one-half the mass of the radioactive substance remains after one half-life.

(D) The half-life of an atom does not change when the atom is incorporated into a compound.

(E) The half-life of a particular substance does not change with time or temperature.

Questions 280–285 refer to the reaction of nitrogen monoxide (nitric oxide) and oxygen and the following data.

280. The rate law for this reaction is:

(A) Rate = k [NO][O₂]

(B) Rate = k [NO][O₂]²

(C) Rate = k [NO]²[O₂]

(D) Rate = k [NO]²[O₂]²

(E) Rate = k [NO][O₂]^1.25

281. The numerical value for the rate constant (k) is closest to:

(A) 5.9 × 10⁻²

(B) 170

(C) 3 × 10³

(D) 7 × 10³

(E) 1.2 × 10⁵

282. The unit of the rate constant (k) is:

(A) sec⁻¹

(B) L mol⁻¹ sec⁻¹

(C) L²mol⁻² sec⁻¹

(D) L³mol⁻³ sec⁻¹

(E) L⁴mol⁻⁴ sec⁻¹

283. Increasing the initial concentration of NO fivefold would increase the reaction rate by:

(A) 5 X

(B) 10 X

(C) 25 X

(D) 3,125 X

(E) No substantial margin

284. What would be the reaction rate if the initial concentration of NO was 2 × 10⁻² M and the initial concentration of O₂ was 4 × 10⁻² M?

(A) 3.2 × 10⁻⁵

(B) 8 × 10⁻⁴

(C) 2.3 × 10⁻²

(D) 1.1 × 10⁻¹

(E) 5.7

285. Which of the following is a correct statement about reaction order?

(A) Reaction order must be a whole number.

(B) Reaction order can be determined mathematically using only coefficients of the balanced reaction equation.

(C) Reaction order can change with increasing temperature.

(D) A second-order reaction must involve at least two reactants.

(E) Reaction order can only be determined experimentally.

286. Properties of a catalyst include all of the following except:

(A) A catalyst that works for one chemical reaction may not work for a different reaction.

(B) A catalyst is not consumed by the reaction it catalyzes.

(C) Catalysts can be solids or gases.

(D) A catalyst will only speed up a chemical reaction in either the forward or reverse direction.

(E) Catalysts speed up chemical reactions by providing an alternate pathway for reaction in which the activated complex is of lower energy.

287. Which of the following can be used to calculate or measure the rate of a chemical reaction?

I. The appearance of product over time

II. The disappearance of one or more substrates over time

III. The rate law

IV. The K_eq (equilibrium constant) and Q (reaction quotient) of the reaction

(A) I and II only

(B) I and III only

(C) I, II, and III only

(D) I, II, and IV only

(E) I, II, III, and IV

288. The reaction of nitric oxide with hydrogen gas at 25°C and 1 atm is represented below. The rate law for this reaction is: rate = k [H₂][NO]².

According to the rate law, which of the following is the best prediction of the rate of this reaction?

(A) The rate of disappearance of NO is always twice as great as the disappearance of H₂.

(B) The rate of disappearance of NO is always four times as great as the disappearance of H₂.

(C) The rate of disappearance of NO is twice as great as the disappearance of H₂ if the concentration of NO is initially twice that of H₂.

(D) The rate of disappearance of NO is four times as fast as that of H₂, but only if the initial concentration of NO is initially twice that of H₂.

(E) The relative disappearances of NO and H₂ cannot be deduced without the value of the rate constant (k).

289. The reaction between nitrogen dioxide and carbon monoxide is represented above. The proposed reaction mechanism is as follows:

Which of the following reaction mechanisms is consistent with the proposed mechanism?

(A) Rate = k [NO₂]

(B) Rate = k [NO₂]²

(C) Rate = k [NO][CO]

(D) Rate = k [NO]²[CO]

(E) Rate = k [CO]

290. The reaction between nitrogen monoxide (commonly called nitric oxide) and bromine is represented above. The proposed reaction mechanism is as follows:

Which of the following reaction mechanisms is consistent with the proposed mechanism?

(A) Rate = k [NO]²

(B) Rate = k [NO][Br₂]

(C) Rate = k [NO][Br₂]²

(D) Rate = k [NO]²[Br₂]

(E) Rate = k [NO]²[Br₂]²

291. The rate constant for a certain chemical reaction at 25°C is 9.0 × 10⁵ L²mol⁻²sec⁻¹. Which of the following must be true regarding this reaction?

(A) This reaction is slower than a reaction that has a rate constant of 9.0 L²mol⁻²sec⁻¹.

(B) This reaction is exothermic.

(C) The rate of this reaction will decrease with increasing temperature.

(D) The reaction order is 3.

(E) Doubling the concentration of reactants will increase the reaction rate by a factor of 8.1 × 10¹⁰.

292. The conversion of ozone, 2 O_{3 (g)} → 3 O_{2 (g)}, obeys the rate law, rate = k [O₃]²[O₂]⁻¹. Which of the following statements is true regarding the rate of the breakdown of ozone (O₃) into molecular oxygen (O₂)?

(A) The catalyst that converts ozone to oxygen is inhibited by oxygen.

(B) The rate at which ozone is converted to oxygen increases as the concentration of oxygen decreases.

(C) There is an inverse square relationship between ozone and oxygen concentrations.

(D) The conversion of oxygen to ozone is faster than the conversion of ozone to oxygen.

(E) The negative reactant order of oxygen indicates that the reaction is at equilibrium and the forward reaction is more favorable.

293. All of the following statements regarding the activated complex are true except:

(A) The energy of the activated complex determines the activation energy of the reaction.

(B) The activated complex represents the highest energy state along the transition path of a chemical reaction.

(C) The activated complex of a chemical reaction is specific to that reaction.

(D) The configuration of atoms in the activated complex of an uncatalyzed reaction is the same as that of a catalyzed reaction, except for the presence of the catalyst.

(E) A reaction in which the energy of the activated complex is very large indicates that the reactants are very thermodynamically stable (as opposed to chemically stable).

Questions 294 and 295 refer to the following graph of a chemical reaction over time.

294. Which of the following is true concerning the reaction at 25°C?

I. The reaction is endothermic.

II. The activation energy (E_a) is approximately 510 kJ mol⁻¹.

III. The magnitude of the difference between energy of the reactants and products is approximately 175 kJ mol⁻¹.

(A) I only

(B) II only

(C) III only

(D) II and III only

(E) I and III only

295. Which of the following is true concerning the effect of adding a catalyst?

(A) The activated complex would form in less than 40 seconds.

(B) It lowers the energy of the products.

(C) It increases the energy of the reactants.

(D) More reactions would occur per second.

(E) The equilibrium would shift to favor the products.

296. A reaction was observed for 30 minutes. Every 5 minutes, the percent of reactant remaining was measured. According to the data in the table above, which of the following most accurately describes the reaction order and half-life of this reaction?

297. The rate laws for the reaction between O₂ and NO is k = [O₂][NO]². If the reaction rate is first measured with O₂ and NO of 2.5 × 10⁻⁴ M each, by what factor will the rate increase if the concentration of O₂ and NO are both increased to 5.0 × 10⁻⁴ each?

(A) 2

(B) 3

(C) 4

(D) 6

(E) 8

Questions 298 and 299 refer to the data below.

298. Consider the data shown above. If the data were obtained from a reaction whose rate law is k = [X][Y]², what would be the expected rate of reaction for Trial 2?

(A) R

(B) 2R

(C) 4R

299. Suppose the data were obtained for a reaction whose rate law is k = [X]²[Y]. What would be the expected rate of reaction for Trial 2?

(A) R

(B) 2R

(C) 4R

300. The units of the rate constant (k) for a reaction that occurs between two second-order reactants is:

(A) sec⁻¹

(B) L mol⁻¹ sec⁻¹

(C) L² mol⁻² sec⁻¹

(D) L³ mol⁻³ sec⁻¹

(E) L⁴ mol⁻⁴ sec⁻¹