chemistry unit 5.1, 5.2, 5.3

After a certain pesticide compound is applied to crops, its decomposition is a first-order reaction with a half-life of 56 days. What is the rate constant, k, for the decomposition reaction?

0.012 day^-1

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:

1

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

Approximately how long did it take for 75 percent of the initial amount of C25H30N3+ (aq) to react?

300s

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 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] ? Responses

5.6 × 10-3 mol L-1 s-1

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 min

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

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

Adding a heterogeneous catalyst to the reaction system

The initial rate of formation of CO2(g from the chemical reaction represented by the equation above was studied in two separate experiments. The table above provides the experimental conditions used. If both experiments are carried out with finely powdered samples of the solid and 50.0mL of HCl(aq), which experiment, if any, will have the faster initial rate of formation of CO2(g) and why?

CO2(g) will be formed at a faster rate in experiment 2 because more H+ particles can react per unit time.

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?

First, 3

The oxidation of NO(g) producing NO2(g) is represented by the chemical equation shown above. The initial concentrations of NO and O2 are given in the table above. The changes in the concentration of NO(g) as a function of time are shown in the following graph. Under the same conditions, one of the following graphs represents the changes in the concentration of O2(g) over the same period of time. Which graph best represents the changes in concentration of O2(g), and why?

Graph 1, because the rate of O2 consumption is half the rate at which NO is consumed; two molecules of NO react for each molecule of O2 that reacts.

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?

Graph of 1/X

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? I. Changes in the partial pressure of H2(g) II. Changes in the particle size of the platinum catalyst III. Changes in the temperature of the reaction system

I, II, III

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?

It is first order in [X].

A student studied the kinetics of the reaction represented above by measuring the concentration of the reactant, X, over time. The data are plotted in the graph below. Which of the following procedures will allow the student to determine the rate constant, k , for the reaction?

Plot ln [X] versus time and determine the magnitude of the slope.

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 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?

Rate=k[NO2]^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.

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], doubling the concentrations of A2 and B will quadruple the rate of the reaction.

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

Strong bonds in reactant molecules

2 N2O5(g) → 4 NO2(g) + O2(g) A sample of N2O5 was placed in an evacuated container, and the reaction represented above occurred. Which of the following correctly describes the reaction?

The decomposition of N2O5 is a first-order reaction.

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.

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−].

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

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?

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

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

An experiment is performed to measure the mass percent of CaCO3(s) in eggshells. Five different samples of CaCO3(s) of known mass react with an excess of 2.0M HCl(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?

Using eggshells that are more finely powdered than those used in the original experiment

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.

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

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 kfor the reaction based on the information in the plot of ln[H2O2] versus time (t) ?

k = -(slope of plot)

The rate constant (k) for the decay of the radioactive isotope I-131 is 3.6×10−3 hours−1. The slope of which of the following graphs is correct for the decay and could be used to confirm the value of k?

ln[I-131]

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