unit 5 ap chem

2 A(g) + B(g) → 2 C(g) When the concentration of substance B in the reaction above is doubled, all other factors being held constant, it is found that the rate of the reaction remains unchanged. The most probable explanation for this observation is that

C

H3AsO4 + 3 I- + 2 H3O+ → H3AsO3 + I3- + H2O The oxidation of iodide ions by arsenic acid in acidic aqueous solution occurs according to the stoichiometry shown above. The experimental rate law of the reaction is: Rate = k[H3AsO4] [I-] [H3O+] According to the rate law for the reaction, an increase in the concentration of hydronium ion has what effect on this reaction?

A

H3AsO4 + 3 I- + 2 H3O+ → H3AsO3 + I3- + H2O The oxidation of iodide ions by arsenic acid in acidic aqueous solution occurs according to the stoichiometry shown above. The experimental rate law of the reaction is: Rate = k[H3AsO4] [I-] [H3O+] What is the order of the reaction with respect to I-?

A

C2H2 (g) + H2(g) -> C2H6 (g) Which of the following will most likely increase the rate of the reaction represented above?

B

The graph above shows the results of a study of the reaction of X with a large excess of Y to yield Z. The concentrations of X and Y were measured over a period of time. According to the results, which of the following can be concluded about the rate law for the reaction under the conditions studied?

B

The half-life of 55Cr is about 2.0 hours. The delivery of a sample of this isotope from the reactor to a certain laboratory requires 12 hours. About what mass of such material should be shipped in order that 1.0 mg of 55Cr is delivered to the laboratory?

B

Gaseous cyclobutene undergoes a first-order reaction to form gaseous butadiene. At a particular temperature, the partial pressure of cyclobutene in the reaction vessel drops to one-eighth its original value in 124 seconds. What is the half-life for this reaction at this temperature?

C

The gas-phase reaction A2(g)+B2(g)→2 AB(g) is assumed to occur in a single step. Two experiments were done at the same temperature inside rigid containers. The initial partial pressures of A2 and B2 used in experiment 1 were twice the initial pressures used in experiment 2. Which statement provides the best comparison of the initial rate of formation of AB in experiments 1 and 2 ?

C

Which of the following best describes the role of the spark from the spark plug in an automobile engine?

C

5 H2O2(aq) + 2 MnO4-(aq) + 6 H+(aq) → 2 Mn2+(aq) + 8 H2O(l) + 5 O2(g) In a titration experiment, H2O2(aq) reacts with aqueous MnO4-(aq) as represented by the equation above. The dark purple KMnO4 solution is added from a buret to a colorless, acidified solution of H2O2(aq) in an Erlenmeyer flask. (Note: At the end point of the titration, the solution is a pale pink color.) At a certain time during the titration, the rate of appearance of O2(g) was 1.0 x 10-3 mol/(L⋅s). What was the rate of disappearance of MnO4- at the same time?

D

A kinetics experiment is set up to collect the gas that is generated when a sample of chalk, consisting primarily of solid CaCO3, is added to a solution of ethanoic acid, CH3COOH. The rate of reaction between CaCO3 and CH3COOH is determined by measuring the volume of gas generated at 22oC and 1 atm as a function of time. Which of the following experimental conditions is most likely to increase the rate of gas production?

D

Step 1: Cl(g) + O3(g) → ClO(g) + O2(g) Step 2: ClO(g) + O(g) → Cl(g) + O2(g) A proposed mechanism for destruction of ozone gas in the stratosphere is represented above. Which of the following is evidence that the mechanism is occurring?

A

Step 1:?(slow)Step 2:NO3(g)+CO(g)→NO2(g)+CO2(g)(fast)Overall:NO2(g)+CO(g)→NO(g)+CO2(g) A two-step reaction mechanism is proposed for a gas-phase reaction, as represented above. Which of the following correctly identifies both the chemical equation for step 1 and the rate law for the overall reaction?

A

The proposed rate-determining step for a reaction is 2 NO2(g)→NO3(g)+NO(g). The graph above shows the distribution of energies for NO2(g) molecules at two temperatures. Based on the graph, which of the following statements best explains why the rates of disappearance of NO2(g) are different at temperature 2 and temperature 1 ?

A

Step 1:NO2(g)+F2(g)⇄NO2F2(g)(fast)Step 2:NO2F2(g)→NO2F(g)+F(g)(slow)Step 3:F(g)+NO2(g)→NO2F(g)(fast) A proposed mechanism for the chemical reaction 2NO2(g)+F2(g)→2NO2F(g)is shown above. Which of the following rate laws is consistent with this mechanism?

A (rate = k[NO2][F2])

Step 1:H2(g)+ICl(g)→HI(g)+HCl(g)H2(g)⁢+ICl(g)→HI(g)+HCl(g)(slow)Step 2:HI(g)+ICl(g)→HCl(g)+I2(g)HI(g)⁢+ICl(g)→HCl(g)+I2(g)(fast) Which of the following represents a rate law for the overall reaction that is consistent with the proposed mechanism?

A (rate=k[H2][ICl]

2NO(g) + O2(g)→N2O2(g) A possible mechanism for the overall reaction represented above is the following. NO(g) + NO(g) → N2O2(g) slow N2O2(g) + O2(g) → 2NO2(g) fast Which of the following rate expressions agrees best with this possible mechanism?

A (rate=k[NO]^2)

A reaction was observed for 20 days and the percentage of the reactant remaining after each day was recorded in the table above. Which of the following best describes the order and the half-life of the reaction?

A (reaction order: first, half-life: 3 days)

2 H2O2(aq) → 2 H2O(l) + O2(g) ΔH° = −196 kJ/molrxn The decomposition of H2O2(aq) is represented by the equation above. A student monitored the decomposition of a 1.0 L sample of H2O2(aq) at a constant temperature of 300. K and recorded the concentration of H2O2 as a function of time. The results are given in the table below. Which of the following statements is a correct interpretation of the data regarding how the order of the reaction can be determined?

B

The rate law for the reaction represented by the equation above is rate = k[NO2][F2]. Which of the following could be the first elementary step of a two-step mechanism for the reaction if the first step is slow and the second step is fast?

B (NO2 (g) + F2 (g) -> NO2F (g) + F (g)

NO2(g) + CO(g) → NO(g) + CO2(g) The reaction between NO2(g) and CO(g) is represented above. The elementary steps of a proposed reaction mechanism are represented below. Step 1: 2 NO2(g) → NO(g) + NO3(g) (slow) Step 2: NO3(g) + CO(g) → NO2(g) + CO2(g) (fast) Which of the following is the rate law for the overall reaction that is consistent with the proposed mechanism?

B (Rate = k [NO2]^2)

2H2(g)+2NO(g)→N2(g)+2H2O(g) For the chemical reaction represented above, the following mechanism is proposed. Step 1:2NO(g)⇌N2O2(g)(fast equilibrium)Step 2:N2O2(g)+H2(g)→N2O(g)+H2O(g)(slow)Step 3:N2O(g)+H2(g)→N2(g)+H2O(g)(fast) Which of the following initial rate law expressions is consistent with this proposed mechanism?

C (rate=k[H2][NO]^2)

2 NO(g) + O2(g) → 2 NO2(g) Consider the following mechanism for the reaction represented above. Step 1: 2 NO ⇄ N2O2 (fast reversible) Step 2: N2O2 + O2 → 2 NO2 (slow) Which of the following statements is true?

D

Relatively slow rates of chemical reaction are associated with which of the following?

D

Which of the following best helps explain why an increase in temperature increases the rate of a chemical reaction?

D

The particle models shown above represent a proposed two-step mechanism for the destruction of ozone (O3O3) in the upper atmosphere. Based on the proposed mechanism, what is the balanced chemical equation for the overall reaction?

D (2O3(g)→3O2(g))

2 N2O5(g) → 4 NO2(g) + O2(g) A sample of N2O5 was placed in an evacuated container, and the reaction represented above occurred. The value of PN2O5, the partial pressure of N2O5(g), was measured during the reaction and recorded in the table below. Time (min) PN2O5 (atm)ln(PN2O5)1PN2O5(atm−1)01505.00.0067100754.30.013200383.60.027300192.90.053 Which of the following correctly describes the reaction?

B

2N2O5(g) → 4NO2(g) + O2(g) A sample of N2O5 was placed in an evacuated container, and the reaction represented above occurred. The value of PN2O5, the partial pressure of N2O5(g), was measured during the reaction and recorded in the table below. Which of the following correctly describes the reaction?

B

Consider the reaction represented by the equation 2 X + 2 Z → X2Z2. During a reaction in which a large excess of reactant X was present, the concentration of reactant Z was monitored over time. A plot of the natural logarithm of the concentration of Z versus time is shown in the figure above. The order of the reaction with respect to reactant Z is

B

If 87.5 percent of a sample of pure 131I decays in 24 days, what is the half-life of 131I?

B

NO(g) + NO3(g) → 2 NO2(g) rate = k[NO][NO3] The reaction represented above occurs in a single step that involves the collision between a particle of NO and a particle of NO3. A scientist correctly calculates the rate of collisions between NO and NO3 that have sufficient energy to overcome the activation energy. The observed reaction rate is only a small fraction of the calculated collision rate. Which of the following best explains the discrepancy?

B

Step 1: NO(g) + O3(g) → NO2(g) + O2(g) Step 2: NO2(g) + O(g) → NO(g) + O2(g) A reaction mechanism for the destruction of ozone, O3(g), is represented above. In the overall reaction, NO(g) is best described as

B

Step 1:H2(g)+ICl(g)→HI(g)+HCl(g)H2(g)⁢+ICl(g)→HI(g)+HCl(g)(slow)Step 2:HI(g)+ICl(g)→HCl(g)+I2(g)HI(g)⁢+ICl(g)→HCl(g)+I2(g)(fast) The reaction is carried out at constant temperature inside a rigid container. Based on this mechanism, which of the following is the most likely reason for the different rates of step 1 and step 2 ?

B

The initial-rate data in the table above were obtained for the reaction represented below. What is the experimental rate law for the reaction? 2 NO(g) + O2(g) → NO2(g)

B

The isomerization of cyclopropane to propylene is a first-order process with a half-life of 19 minutes at 500oC. The time it takes for the partial pressure of cyclopropane to decrease from 1.0 atmosphere to 0.125 atmosphere at 500oC is closest to

B

The particle models shown above represent a proposed two-step mechanism for the destruction of ozone (O3O3) in the upper atmosphere. Based on the proposed mechanism, which of the following best describes the concentration of the species represented above as the reaction occurs?

B

Which of the following statements best explains why an increase in temperature of 5-10 Celsius degrees can substantially increase the rate of a chemical reaction?

B

NO(g) and O2(g) react to form NO2(g). The rate law of the reaction is rate=k[NO]2[O2]. If the reaction occurs in a single elementary step that is a three-body molecular collision, then which of the following is the equation for the elementary step?

B (2NO+O2→2NO2)

Step 1: Ce4+ + Mn2+ → Ce3+ + Mn3+ Step 2: Ce4+ + Mn3+ → Ce3+ + Mn4+ Step 3: Mn4+ + Tl+ → Tl3+ + Mn2+ The proposed steps for a catalyzed reaction between Ce4+ and Tl+ are represented above. The products of the overall catalyzed reaction are

B (Ce^(3+) and TI^(3+))

When free Cl(g) atoms encounter O3(g) molecules in the upper atmosphere, the following reaction mechanism is proposed to occur. Which of the following rate laws for the overall reaction corresponds to the proposed mechanism?

B (Rate = k[Cl][O3])

Br2(g)+2NO(g)→2NOBr(g) The reaction represented by the equation above has the following proposed mechanism. Step 1:NO(g)+Br2(g)⇌NOBr2(g)(fast equilibrium)Step 2:NOBr2(g)+NO(g)→2NOBr(g)(slow) Based on the information, which of the following is the initial rate law for the reaction?

B (Rate=k[Br2][NO]2)

2HBr(g)+O2(g)→H2O2(g)+Br2(g) Based on a kinetics study of the reaction represented by the equation above, the following mechanism for the reaction is proposed. Step 1:HBr(g)+O2(g)→HO2Br(g)(slow)Step 2:HO2Br(g)+HBr(g)→2HOBr(g)(fast)Step 3:2HOBr(g)→H2O2(g)+Br2(g)(fast) Which of following rate laws is consistent with the proposed mechanism?

B (Rate=k[HBr][O2])

The data from a study of the decomposition of NO2(g) to form NO(g) and O2(g) are given in the table above. Which of the following rate laws is consistent with the data?

B (rate = k[NO2]^2

The data in the table above were obtained for the reaction X + Y → Z. Which of the following is the rate law for the reaction?

B (rate = k[Y]^2

Cl−(aq) + ClO−(aq) + 2 H+(aq) → Cl2(g) + H2O(l) What effect will increasing [H+] at constant temperature have on the reaction represented above?

C

Cu(s) + 4 HNO3(aq) → Cu(NO3)2(aq) + 2 NO2(g) + 2 H2O(l) Each student in a class placed a 2.00 g sample of a mixture of Cu and Al in a beaker and placed the beaker in a fume hood. The students slowly poured 15.0 mL of 15.8 M HNO3(aq) into their beakers. The reaction between the copper in the mixture and the HNO3(aq) is represented by the equation above. The students observed that a brown gas was released from the beakers and that the solutions turned blue, indicating the formation of Cu2+(aq). The solutions were then diluted with distilled water to known volumes. In one student's experiment the reaction proceeded at a much slower rate than it did in the other students' experiments. Which of the following could explain the slower reaction rate?

C

Two samples of Mg(s) of equal mass were placed in equal amounts of HCI(aq) contained in two separate reaction vessels. Particle representations of the mixing of Mg(s) and HCI(aq) in the two reaction vessels are shown in Figure 1 and Figure 2 above. Water molecules are not included in the particle representations. Which of the reactions will initially proceed faster, and why?

C

X2 + Y2 → X2Y2 rate = k[X2] A reaction and its experimentally determined rate law are represented above. A chemist proposes two different possible mechanisms for the reaction, which are given below. Mechanism 1Mechanism 2 X2 → 2 X (slow) X2 → 2 X (slow)X + Y2 → XY2 (fast) X + Y2 → XY + Y (fast)X + XY2 → X2Y2 (fast)X + XY → X2Y (fast) X2Y + Y → X2Y2 (fast) Based on the information above, which of the following is true?

C

The particle models shown above represent a proposed two-step mechanism for the destruction of ozone (O3O3) in the upper atmosphere. Based on the models, which of the following represents a species that acts as a catalyst for the reaction?

C (1 Cl)

The reaction between C25H30N3+ (aq) and OH-(aq), as represented above, is first order with respect to C25H30N3+ (aq) in the presence of excess OH-(aq). A 10.0 mL sample of 0.10 M NaOH(aq) is mixed with a 10.0 mL sample of 2.5 x 10-5 M C25H30N3+(aq). A 5.0 mL sample of the mixture is quickly transferred to a clean cuvette and placed in a spectrophotometer, and the progress of the reaction is measured. The data are given in the table below. Approximately how long did it take for 75 percent of the initial amount of C25H30N3+ (aq) to react?

C (300s)

Step 1. N2H2O2 ⇄ N2HO2- + H+ (fast equilibrium) Step 2. N2HO2- → N2O + OH- (slow) Step 3. H+ + OH- → H2O (fast) Nitramide, N2H2O2, decomposes slowly in aqueous solution. This decomposition is believed to occur according to the reaction mechanism above. The rate law for the decomposition of nitramide that is consistent with this mechanism is given by which of the following?

C (Rate = k[N2H2O2]/[H+])

2 NOBr(g) → 2 NO(g) + Br2(g) The equation above represents an elementary step in a chemical reaction. Which of the following is the correct expression for the rate law of the elementary step?

C (Rate = k[NOBr]2)

A kinetics experiment is set up to collect the gas that is generated when a sample of chalk, consisting primarily of solid CaCO3, is added to a solution of ethanoic acid, CH3COOH. The rate of reaction between CaCO3 and CH3COOH is determined by measuring the volume of gas generated at 25oC and 1 atm as a function of time. Which of the following experimental conditions is most likely to increase the rate of gas production?

D

An experiment is performed to measure the mass percent of CaCO3(s)CaCO3(s) in eggshells. Five different samples of CaCO3(s)CaCO3(s) of known mass react with an excess of 2.0MHCl(aq)2.0MHCl(aq) in identical sealed, rigid reaction vessels. The pressure of the gas produced is measured with a pressure gauge attached to the reaction vessel. Since the reaction is exothermic, the reaction system is cooled to its original temperature before the pressure is recorded. The experimental data are used to create the calibration line below. Which of the following modifications will increase the rate of the reaction the most?

D

The table above shows the results from a rate study of the reaction X + Y → Z. Starting with known concentrations of X and Y in experiment 1, the rate of formation of Z was measured. If the reaction was first order with respect to X and second order with respect to Y, the initial rate of formation of Z in experiment 2 would be

D (2R)

X + 2 Y → Z + 3 Q For the reaction represented above, the initial rate of decrease in [X] was 2.8 × 10-3 mol L-1 s-1. What was the initial rate of decrease in [Y] ?

D (5.6...)

Rate = k[M][N]2 The rate of a certain chemical reaction between substances M and N obeys the rate law above. The reaction is first studied with [M] and [N] each 1 x 10-3 molar. If a new experiment is conducted with [M] and [N] each 2 x 10-3 molar, the reaction rate will increase by a factor of

D (8)

The particle models shown above represent a proposed two-step mechanism for the destruction of ozone (O3O3) in the upper atmosphere. Based on the proposed mechanism, which of the following is the rate-law expression for the destruction of O3 ?

D (Rate=k[O3][Cl])

NO(g) + NO3(g) → 2 NO2(g) The reaction between NO(g) and NO3(g) is represented by the equation above. Which of the following orientations of collision between NO(g) and NO3(g) is most likely to be effective?

D (grey N hitting white O)

X → products Pure substance X decomposes according to the equation above. Which of the following graphs indicates that the rate of decomposition is second order in X ?

D (increasing graph image; 1/X)

The rate law for the reaction of nitrogen dioxide and chlorine is found to be rate = k [NO2]2[Cl2]. By what factor does the rate of the reaction change when the concentrations of both NO2 and Cl2 are doubled?

E

If the oxygen isotope 20O has a half-life of 15 seconds, what fraction of a sample of pure 20O remains after 1.0 minute?

E (1/16)

C2H4(g) + H2(g) −→−−−platinum C2H6(g) C2H4(g) is reduced by H2(g) in the presence of a solid platinum catalyst, as represented by the equation above. Factors that could affect the rate of the reaction include which of the following? Changes in the partial pressure of H2(g) Changes in the particle size of the platinum catalyst Changes in the temperature of the reaction system

E (I, II, and III)

Factors that affect the rate of a chemical reaction include which of the following? I. Frequency of collisions of reactant particles II. Kinetic energy of collisions of reactant particles III. Orientation of reactant particles during collisions

E (I, II, and III)