AP Chemistry Unit 5 Progress Check

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.

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−O bond as long as they possess enough energy to overcome the activation energy barrier.

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?

H2SO4, because it is consumed in the first step of the mechanism and regenerated in a later step.

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?

Model representing NNO

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

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].

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+O2 , 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] .

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 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)

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.

16 M/s

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.

First Order

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 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.

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]

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

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]

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]

Reaction A: O+O→O2 Reaction B: C2H4+C2H4→C4H8 Reaction C: CO+O2→CO2+O Reaction D: CH3I+Br−→CH3Br+I−

Reaction A, because the electron clouds of the O atoms are distributed symmetrically.

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 CH3I is doubled while keeping the concentration of NaOH 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.

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 energy to reactant particles to increase their rate of reaction compared to their rate of reaction in the first chemist's experiments.

Zn(s)+2 HCl(aq)→ZnCl2(aq)+H2(g) Zn(s)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) has a greater surface area for the reaction to take place.

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]

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. On the basis of the data in the graph, which of the following best represents the rate law for the catalyzed decomposition of NH3(g)?

rate=k

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]

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]