Chapter 5 Chem ☹️

After a certain pesticide compound is applied to crops, its decomposition is a first-order reaction with a half-life of 32.5 32.5 days. What is the rate constant, k, for the decomposition reaction?

0.0213 day^-1

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? 1. Changes in the partial pressure of H2(g) 2. Changes in the particle size of the platinum catalyst 3. Changes in the temperature of the reaction system

1, 2, and 3

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?

1/16

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

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?

300 s

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?

4.0 x 10-4 mol/(L⋅s)

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

5.6 x 10^-3 mol L^-1 s^-1

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] ?

5.6 × 10-3 mol L-1 s-1

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

2X+Y2→X2Y2 A chemist is studying the reaction between the gaseous chemical species X and Y2, represented by the equation above. Initial rates of reaction are measured at various concentrations of reactants. The results are recorded in the following table. Based on the information above, determine the initial rate of disappearance of X in experiment 1.

64M/s

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

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?

8

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.

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. Based on the information above, which of the following is true?

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

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

Ce3+ and Tl3+

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 (Y= 1/x; Line positive)

Two solid reactants of varying particle size are combined in a vessel. Assuming that the same mass of each reactant is used in each case, which of the following represents the conditions that will result in the fastest reaction rate?

D (small, black dots, temp 950 C)

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?

Decreasing the particle size of the CaCO3 by grinding it into a fine powder

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 25 degrees celsius and 1 atm as a function if time. Which of the following experimental conditions is most likely to increase the rate of gas production?

Decreasing the particle size of the CaCO3 by grinding it into a fine powder

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?

Decreasing the particle size of the CaCO3 by grinding it into a fine powder

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

C12H22O11(aq)+H2O(l)→2C6H12O6(aq) The chemical equation shown above represents the hydrolysis of sucrose. Under certain conditions, the rate is directly proportional to the concentration of sucrose. Which statement supports how a change in conditions can increase the rate of this reaction?

Increasing the concentration of sucrose will increase the rate of hydrolysis by increasing the frequency of the collisions between the sucrose and the water molecules.

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 Y2 molecules will have the minimum energy to overcome the activation energy barrier.

The decomposition of O3(g) in the upper atmosphere is represented by the equation above. The potential energy in the upper atmosphere is diagram for the decomposition of O3(g) in the presence and absence of NO(g) is given below. Which of the following mechanisms for the catalyzed reaction is consistent with the equation and diagram above?

O3(g) + NO(g) → NO2(g) + O2(g) slow NO2(g) + O(g) → NO(g) + O2(g) fast

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?

Rate = k[Cl][O3]

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?

Rate = k[N2H2O2]/[H+]

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?

Rate = k[NO]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

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] , because the initial rate quadrupled when [NO] was doubled and doubled when [Cl2] was doubled

2X+Y2→X2Y2 A chemist is studying the reaction between the gaseous chemical species X and Y2, represented by the equation above. Initial rates of reaction are measured at various concentrations of reactants. The results are recorded in the following table. Given the information in the table above, which of the following is the experimental rate law?

Rate=k[X][Y2]

2H2(g)+2NO(g)→N2(g)+2 H2O(g) The experimental rate law for the reaction represented above is rate=k[H2][NO]2 . Which of the following proposed mechanisms is consistent with the rate law?

Step 1: 2NO⇄N2O2 fast Step 2: H2+N2O2→N2O+H2O slow Step 3: H2+N2O→N2+H2O fast

The slowest step in a reaction mechanism requires the collision represented above to occur. Which of the following most likely indicates how the addition of a solid catalyst could increase the rate of the reaction?

The catalyst could adsorb one of the particles, making a successful (reaction-producing) collision with the other particle more likely.

A student performed an experiment to study the factors that affect the rate of the first-order catalytic decomposition of H2O2(aq), represented above. The student monitored the volume of O2(g) produced over time as the reaction proceeded. The data from two trials are plotted in the graph above. Which of the following best explains the results of trial 2 compared with those of trial 1

The concentration of H2O2(aq) was lower in trial 2 than it was in trial 1

2 H2O2(aq)−→−−KI(s)2 H2O(l)+O2(g) Rate=k[H2O2] A student performed an experiment to study the factors that affect the rate of the first-order catalytic decomposition of H2O2(aq) , represented above. The student monitored the volume of O2(g) produced over time as the reaction proceeded. The data from two trials are plotted in the graph above. Which of the following best explains the results of trial 2 compared with those of trial 1?

The concentration of H2O2(aq)) was lower in trial 2 than it was in trial 1

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.

The decomposition of N2O5 is a first- order rxn

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?

The frequency of collisions between H+(aq) ions and ClO−(aq) ions will increase.

2NO(g)+2H2(g)→N2(g)+2H2O(g) The information in the data table above represents two different trials for an experiment to study the rate of the reaction between NO(g) and H2(g), as represented by the balanced equation above the table. Which of the following statements provides the correct explanation for why the initial rate of formation of N2 is greater in trial 2 than in trial 1? Assume that each trial is carried out at the same constant temperature.

The frequency of collisions between reactant molecules is greater in trial 2 than it is in trial 1.

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); the rate law for step 2 is rate=k[HI][ICl]

The following questions relate to the below information. XY2 → X + Y2 The equation above represents the decomposition of a compound XY2. The diagram below shows two reaction profiles (path one and path two) for the decomposition of XY2. Which of the following most likely accounts for the difference between reaction path one and reaction path two?

The presence of a catalyst in path two

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].

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−]

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?

The reaction in Figure 2, because more Mg atoms are exposed to HCI(aq) in Figure 2 than in Figure 1

Two samples of Mg of equal mass were placed in equal amounts of HCl contained in two separate reaction vessels. Particle representations of the mixing of Mg and HCl in the two reaction vessels are showing figure 1 and figure 2 above. Water molecules are not included in the particle representations. Which if the reactions will initially proceed faster, and why?

The reaction in Figure 2, because more Mg atoms are exposed to HCl in Figure 2 than in Figure 1

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. The figure shows a table with 2 columns and 5 rows. The top row contains the column labels, from left to right Which of the following statements is a correct interpretation of the data regarding how the order of the reaction can be determined?

The reaction is first order if the plot of ln [H2O2] versus time is a straight line.

A second chemist repeated the three experiments and observed that the reaction rates were considerably greater than those measured by the first chemist, even though the concentrations of the reactants and the temperature in the laboratory were the same as they were for the first chemist. Which of the following is the best pairing of a claim about a most likely cause for the greater rates measured by the second chemist and a valid justification for that claim?

The second chemist must have added a catalyst for the reaction, thus providing a different reaction pathway for the reactant particles to react with an activation energy that was lower than that of the uncatalyzed reaction in the first chemist's experiments.

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

The spark supplies some of the energy of activation for the combustion reaction.

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?

The two reactant particles must collide with a particular orientation in order to react.

A 0.35 g sample of Li(s) is placed in an Erlenmeyer flask containing 100 mL of water at 25°C. A balloon is placed over the mouth of the flask to collect the hydrogen gas that is generated. After all of the Li(s) has reacted with H2O(l), the solution in the flask is added to a clean, dry buret and used to titrate an aqueous solution of a monoprotic acid. The pH curve for this titration is shown in the diagram below Which of the following changes will most likely increase the rate of reaction between Li(s) and water?

Using a 0.35 g sample of Li(s) cut into small pieces

In order to determine the order of the reaction represented below, the initial rate if formation od XY2 is measuring different initial values of [X] and [Y]. The results of the experare shown in the table below. X + 2Y -> XY2 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

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 catalyst

The role of a catalyst in a chemical reaction is to

lower the activation energy for the reaction

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?

order: 1st; half life: 3 days

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