Kinetics Practice Test

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? A

1/16

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 ?

1/x up

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?

2NO+O2→2NO2

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

2R

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?

41.3 sec

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

57 minutes

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?

64 mg

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

8

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

8 days

Which of the following will most likely increase the rate of the reaction represented above?

Adding a heterogeneous catalyst to the reaction system

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

At higher temperatures, high-energy collisions happen more frequently.

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]

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?

Both mechanism 1 and mechanism 2 are consistent with the rate law.

H-H 430 Cl-Cl 240 H-Cl 430 Based on the bond energies shown in the table above, which of the following diagrams best represents the change in energy as the reaction represented below proceeds? H2(g)+ Cl2(g)→2HCl(g)

H2 Cl2 190

The energy diagram for the reaction X + Y → Z is shown above. The addition of a catalyst to this reaction would cause a change in which of the indicated energy differences?

I and II only

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

I, II, and III

The energy distribution profile (Curve C) for the Y2 molecules is shown in the graph above for the reaction X+Y2→XY2 when it is done under certain experimental conditions. Line A represents the most probable energy of the Y2 molecules, and Line B represents the activation energy. Which of the following changes should be made to the graph to explain the increase in the rate of the reaction if the only change in experimental conditions is the addition of a catalyst?

Line B will move to the left because a larger fraction of the Y2Y2 molecules will have the minimum energy to overcome the activation energy barrier.

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)

Rate = k[NO][O2]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?

Rate = k[Y]2

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?

Rate=k[Br2][NO]2

2HO2(g)→H2O2(g)+O2(g) The reaction represented by the chemical equation shown above occurs in Earth's atmosphere. In an experiment, [HO2] was monitored over time and the data plotted as shown in the following graph. Based on the information, which of the following is the rate law expression for the reaction?

Rate=k[HO2]2

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?

Rate=k[NO2][F2]

2NO(g)+Cl2(g)→2NOCl(g) Experiment[NO][Cl2]Initial Rate of NOCl Formation(Ms−1)10.02500.05104.55×10−520.02500.10209.10×10−530.05000.05101.82×10−4 The initial rates of the reaction represented by the equation shown above were measured for different initial concentrations of NO(g) and Cl2(g). Based on the data given in the table above, which of the following is the rate law expression for the reaction, and why?

Rate=k[NO]2[Cl2]Rate=k[NO]2[Cl2], because the initial rate quadrupled when [NO][NO] was doubled and doubled when [Cl2][Cl2] was doubled.

Trial[A2][B]Initial rate (Ms−1)10.100.502.5×10−420.200.505.0×10−430.300.055.0×10−540.300.101.0×10−4 An experiment was conducted to determine the rate law for the reaction A2(g)+B(g)→A2B(g). The table above shows the data collected. Based on the data in the table, which statement is correct?

Since the rate law can be expressed as rate=k[A2][B]rate=k[A2][B], doubling the concentrations of A2A2 and BB will quadruple the rate of the reaction.

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?

The decomposition of N2O5 is a first-order reaction.

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?

The rate law that is consistent with the mechanism is rate = k[NO]2[O2].

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 ?

The initial rate of formation of ABAB is faster in experiment 1 than in experiment 2 because at a higher pressure the collisions between A2A2 and B2B2 molecules would have been more frequent, increasing the probability of a successful collision.

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?

The number of effective collisions between reactant particles is increased.

Step 1:H2(g)+ICl(g)→HI(g)+HCl(g)(slow)Step 2:HI(g)+ICl(g)→HCl(g)+I2(g)(fast) Which of the following represents the overall chemical equation for the reaction and the rate law for elementary step 2 ?

The overall reaction is H2(g)+2ICl(g)→2HCl(g)+I2(g)H2(g)+2ICl(g)→2HCl(g)+I2(g); the rate law for step 2 is rate=k[HI][ICl]rate=k[HI][ICl].

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?

The presence of Cl(g) increases the rate of the overall reaction.

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?

The rate of reaction increases.

S2O82−(aq)+3I−(aq)→2SO42−(aq)+I3−(aq) In aqueous solution, the reaction represented by the balanced equation shown above has the experimentally determined rate law: rate=k[S2O82−][I−]. If the concentration of [S2O82−] is doubled while keeping [I−] constant, which of the following experimental results is predicted based on the rate law, and why?

The rate of reaction will double, because the rate is directly proportional to [S2O82−][S2O82−].

C12H22O11+H2O→2C6H12O6 The hydrolysis of sucrose is represented by the chemical equation above. This reaction is extremely slow in aqueous solution. However, when sucrase is added as shown in the diagram, the rate of the reaction is about 6,000,000 times faster. Based on this information, which of the following best explains the large increase in the rate of hydrolysis that occurs with the addition of sucrase?

The reaction proceeds through a different reaction path with a lower activation energy in which the sucrase-sucrose complex is formed as an intermediate.

X(g) + 2 Y(g) → XY2(g) In order to determine the order of the reaction represented above, the initial rate of formation of XY2 is measured using different initial values of [X] and [Y]. The results of the experiment are shown in the table below. In trial 2 which of the reactants would be consumed more rapidly, and why?

Y, because the rate of disappearance will be double that of X.

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 A

a catalyst

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 reaction energy profiles best corresponds to the proposed mechanism?

high xhigh low medium xlow

H2O2→H2O+12O2 Hydrogen peroxide decomposes to produce water and oxygen according to the equation above. An experimentally determined graph for the first-order decomposition of hydrogen peroxide is provided below. Which of the following best identifies the rate constant k for the reaction based on the information in the plot of ln[H2O2] versus time (t) ?

k=−(slope of plot)

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

substance B is not involved in the rate-determined step of the mechanism, but is involved in subsequent steps