chem unit 5
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 two diagrams above represent collisions that take place at the same temperature between a CO molecule and an NO2 molecule. The products are CO2 and NO. Which diagram most likely represents an effective collision, and why?
Diagram 1 represents an effective collision because the two molecules have the proper orientation to form a new C−OC−O bond as long as they possess enough energy to overcome the activation energy barrier.
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?
Rate=k[H2][NO]2Rate=k[H2][NO]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]
Relatively slow rates of chemical reaction are associated with which of the following?
Strong bonds in reactant molecules
Step 1:H2O2+I−→IO−+H2O Step 2:H2O2+IO−→H2O+O2+I− The mechanism for a chemical reaction is shown above. Which of the following statements about the overall reaction and rate laws of the elementary reactions is correct?
The chemical equation for the overall reaction is 2 H2O2→2 H2O+O22 , and the rate law for elementary step 1 is rate=k[H2O2][I−]\
Step 1:N2O5→NO2+NO3(slow) Step 2:NO2+NO3→NO2+NO+O2(fast) Step 3:NO+N2O5→3 NO2(fast) A proposed reaction mechanism for the decomposition of N2O5(g) is shown above. Based on the proposed mechanism, which of the following correctly identifies both the chemical equation and the rate law for the overall reaction?
The chemical equation for the overall reaction is 2N2O5(g)→4NO2(g)+O2(g) and the rate law is rate=k[N2O5].
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
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.
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+
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]
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
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
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?
Rate=k[HBr][O2]Rate=k[HBr][O2]
The diagram above shows the distribution of molecular energies for equimolar samples of a reactant at different temperatures. Based on the diagram, at which temperature will the reactant be consumed at the fastest rate, and why?
At T4, because a larger fraction of the molecules have an energy that is equal to or greater than the activation energy.
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
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.
Which of the following best describes the elementary step(s) in the reaction mechanism represented in the diagram above?
Two steps: Step 1: 2X(g)→X2(g) Step 2:X2(g)+Y(g)→X2Y(g)
Step 1:2NO⇄(NO)2(fast) Step 2:(NO)2+O2⇄2NO2(slow) The elementary steps in a proposed mechanism for the reaction 2 NO(g)+O2(g)→2NO2(g) are represented by the equations above. Which of the following is the rate law for the overall reaction that is consistent with the proposed mechanism?
rate=k[NO]2[O2]
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
Step 1:HCOOH+H2SO4→HCOOH2++HSO4− Step 2:HCOOH2+→HCO++H2O Step 3:HCO++HSO4−→CO+H2SO4 The elementary steps in a proposed mechanism for the decomposition of HCOOH are represented above. Which of the following identifies the catalyst in the overall reaction and correctly justifies the choice?
H2SO4H2SO4, because it is consumed in the first step of the mechanism and regenerated in a later step.
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)
energy difference is 190
The role of a catalyst in a chemical reaction is to
lower the activation energy for the reaction
The diagram above shows the reaction energy profiles for a reaction with and without a catalyst. Which of the following identifies the reaction energy profile for the catalyzed reaction, and why?
Profile Y, because it introduces a different reaction path that reduces the activation energy.
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
H2O2→H2O+1/2O2 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)
Bi 83214→Po 84214+e−1 0 Bismuth-214 undergoes first-order radioactive decay to polonium-214 by the release of a beta particle, as represented by the nuclear equation above. Which of the following quantities plotted versus time will produce a straight line?
ln[Bi]
The diagram above illustrates how the reaction N2(g)+3H2(g)→2NH3(g) occurs on the surface of Ru(s). The rate of this reaction is determined by the amount of energy required to break the bond in N2. This bond is weakened when N2 is adsorbed on Ru(s). Based on this information, which of the following provides the best reason for the use of Ru(s) for the synthesis of NH3 ?
It provides a reaction path with a lower activation energy.
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+]
1
CaCO3(s)+2H+(aq)→Ca2+(aq)+H2O(l)+CO2(g) 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)CO2(g) will be formed at a faster rate in experiment 2 because more H+H+ particles can react per unit time.
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
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? 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, and III
The proposed mechanism for a reaction involves the three elementary steps represented by the particle models shown above. On the basis of this information, which of the following models represents an intermediate in the overall reaction?
N2O
2NO2(g) + F2(g) -> 2NO2F(g) 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?
NO2(g) + F2(g) -> NO2F(g) + F(g)
experiment 1: x 0.10; y 0.30; rate 4.0 * 10^-4 experiment 2: x 0.20; y 0.60; rate 1.6* 10^-3 experiment 3: x 0.20; y 0.30; rate 4.0*10^-4 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 diagram above shows the progress of the chemical reaction for the synthesis of ammonia from its elements. The adsorption of the N2 molecules on the surface of Ru weakens the triple bond between the two N atoms. Based on the diagram, what is the role of Ru in this process?
Ru is a catalyst.
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} vs time (negative slope)
Step 1:2X(g)⇄X2(g)(fast) Step 2:X2(g)+Y(g)→X2Y(g)(slow) The rate law for the hypothetical reaction 2X(g)+Y(g)→X2Y(g) is consistent with the mechanism shown above. Which of the following mathematical equations provides a rate law that is consistent with this mechanism?
rate=k[X]2[Y]
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
2N2O5(g)→4NO2(g)+O2(g) For the reaction represented by the equation above, the concentration of N2O5 was measured over time. The following graphs were created using the data. Based on the graphs above, what is the order of the reaction with respect to N2O5 ?
First order
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] vs time (positive slope)
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
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
first order
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?
2 bumps, both with product lower than reactant
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
When the chemical reaction 2NO(g)+O2(g)→2NO2(g) is carried out under certain conditions, the rate of disappearance of NO(g) is 5.0×10−5 Ms−1. What is the rate of disappearance of O2(g) under the same conditions?
Because two molecules of NONO are consumed per molecule of O2O2, the rate of disappearance of O2(g)O2(g) is 2.5×10−5 Ms−12.5×10−5 Ms−1.
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.
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 O2O2 consumption is half the rate at which NONO is consumed; two molecules of NONO react for each molecule of O2O2 that reacts.
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+]
2NH3(g)−→−−−−catalystN2(g)+3H2(g) The catalyzed decomposition of NH3(g) at high temperature is represented by the equation above. The rate of disappearance of NH3(g) was measured over time for two different initial concentrations of NH3(g) at a constant temperature. The data are plotted in the graph below.
Rate=k
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]2Rate=k[Br2][NO]2
Reaction A:O+O→O2 Reaction B:C2H4+C2H4→C4H8 Reaction C:CO+O2→CO2+O Reaction D:CH3I+Br−→CH3Br+I− The equations shown above represent four elementary reactions. Which of the following identifies the reaction in which the number of successful collisions and reaction rate are independent of the orientation of the reactants and explains why?
Reaction A, because the electron clouds of the OO atoms are distributed symmetrically.
Step 1:H2(g)+ICl(g)→HI(g)+HCl(g)(slow) Step 2: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 ?
The amount of energy required for a successful collision between H2H2 and IClICl is greater than the amount of energy required for a successful collision between HIHI and IClICl.
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?
The chemical equation for step 1 is 2NO2(g)→NO(g)+NO3(g)2NO2(g)→NO(g)+NO3(g), and the rate law is rate=[NO2]2rate=[NO2]2.
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.
O3(g)+O(g)→2O2(g) The decomposition of O3 occurs according to the balanced equation above. In the presence of NO, the decomposition proceeds in two elementary steps, as represented by the following mechanism. Step 1: O3+NO→NO2+O2 (slow) Step 2: NO2+O→NO+O2 (fast) Based on the information, which of the following is the rate law?
Rate=k[O3][NO]
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]rate=k[HI][ICl].
2NO(g)+Cl2(g)→2NOCl(g) 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.
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]
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.
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?
7/30
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
If 87.5 percent of a sample of pure 131I decays in 24 days, what is the half-life of 131I?
8 days
C2H4)g) -> C2H6(g) Which of the following will most likely increase the rate of the reaction represented above?
Adding a heterogeneous catalyst to the reaction system
H2(g)+I2(g)→2HI(g) For the reaction between H2 and I2, shown above, the following two-step reaction mechanism is proposed. Step 1:I2⇄2I(fast equilibrium) Step 2:H2+2I→2HI(slow) What is the rate law expression for this reaction if the second step is rate determining?
Rate=k[H2][I2]
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 Y2Y2 molecules will have the minimum energy to overcome the activation energy barrier. C
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 ?
NO2(g)NO2(g) is consumed at a faster rate at temperature 2 because more molecules possess energies at or above the minimum energy required for a collision to lead to a reaction compared to temperature 1.
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 a rate law for the overall reaction that is consistent with the proposed mechanism?
Rate=k[H2][ICl]Rate=k[H2][ICl]
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 1:2NO2(g)→NO3(g)+NO(g)(slow) Step 2:NO3(g)+CO(g)→NO2(g)+CO2(g)(fast) A proposed two-step mechanism for the chemical reaction NO2(g)+CO(g)→NO(g)+CO2(g) is shown above. Which of the following equations is a correct rate law that is consistent with the elementary steps in the mechanism?
Rate=k[NO2]2
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.
Step 1:?(slow) Step 2:NO2(g)+F(g)→NO2F(g)(fast) Overall:2 NO2(g)+F2(g)→2NO2F(g) The overall reaction represented above is proposed to take place through two elementary steps. Which of the following statements about the chemical equation for step 1 and the rate law for the overall reaction is correct?
The chemical equation for step 1 is NO2(g)+F2(g)→NO2F(g)+F(g), and the rate law for the overall reaction is rate=k[NO2][F2].
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?
The decomposition of N2O5 is a first-order reaction.
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.
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.
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.
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].
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−].
CH3I+NaOH→CH3OH+NaI The rate of the reaction represented by the chemical equation shown above is expressed as rate=k[CH3I][NaOH]. Based on this information, which of the following claims is correct?
The rate of the reaction will double if the concentration of CH3ICH3I is doubled while keeping the concentration of NaOHNaOH constant.
Step 1:H2+IBr→HI+HBr(slow) Step 2:HI+IBr→I2+HBr(fast) A proposed mechanism for the reaction H2+2IBr→I2+2HBr is shown above. Two experiments were performed at the same temperature but with different initial concentrations. Based on this information, which of the following statements is correct?
The rate of the reaction will undergo a 4-fold increase in the experiment in which the initial concentrations of both H2 and IBr were doubled.
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 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.
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. 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.
Zn(s)+2 HCl(aq)→ZnCl2(aq)+H2(g) Zn(s) reacts with HCl(aq) according to the equation shown above. In trial 1 of a kinetics experiment, a 5.0g piece of Zn(s) is added to 100mL of 0.10MHCl(aq). The rate of reaction between Zn(s) and HCl(aq) is determined by measuring the volume of H2(g) produced over time. In trial 2 of the experiment, 5.0g of powdered Zn(s) is added to 100mL of 0.10MHCl(aq). Which trial will have a faster initial rate of reaction and why?
Trial 2, because the sample of Zn(s)Zn(s) has a greater surface area for the reaction to take place.
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
