ap chem 2016

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? a. b. c. d.

a.

A student mixes a 10.0 mL sample of 1.0 M NaOH (aq) with a 10.0 mL sample of 1.0 M HCl (aq) in a polystyrene container. The temperature of the solutions before mixing was 20.0 degrees C. If the final temperature of the mixture is 26.0 degrees C, what is the experimental value of delta H rxn? (Assume that the solution mixture has a specific heat of 4.2 J/(gK) and a density of 1.0 g/mL) a. -50. kJ/mol rxn b. -25 kJ/mol rxn c. -5.0 x 10^4 kJ/mol rxn d. -5.0 x 10^2 kJ/mol rxn

a. -50. kJ/mol rxn

On the basis of the information above, which of the following arranges the binary compounds in order of increasing bond polarity? a. CH4 < SiCl4 < SF4 b. CH4 < SF4 < SiCl4 c. SF4 < CH4 < SiCl4 d. SiCL4 < SF4 < CH4

a. CH4 < SiCl4 < SF4

Which of the following arranges the molecules N2, O2, and F2 in order of their bond enthalpies, from least to greatest? a. F2 < O2 < N2 b. O2 < N2 < F2 c. N2 < O2 < F2 d. N2 < F2 < O2

a. F2 < O2 < N2

2 H2S (g) + CH4 (g) -> <- CS2 (g) + 4 H2 (g) Ke= 3.4 x 10^-4 A 0.10 mol sample of each of the four species in the reaction represented above is injected into a rigid, previously evacuated 1.0 L container. Which of the following species will have the highest concentration when the system reaches equilibrium? a. H2S (g) b. CH4 (g) c. CS2 (g) d. H2 (g)

a. H2S (g)

HX (aq) + Y- (aq) -> <- HY (aq) + X- (aq) Keq>1 a. HX (aq) b. Y- (aq) c. HY (aq) d. X- (aq)

a. HX (aq)

Based on the Ksp values in the table above, a saturated solution of which of the following compounds has the highest [Cl-] a. PbCl2 b. CuCl c. AgCl d. Hg2Cl2

a. PbCl2

A sample of hard, solid binary compound at room temperature did not conduct electricity as a pure solid but became highly conductive when dissolved in water. Which of the following types of interactions is most likely found between the particles in the substance? a. ionic bonds b. metallic bonds c. covalent bonds d. hydrogen bonds

a. ionic bonds

Which of the following statements about the bonds in the reactants and products is more accurate? a. the sum of the bond enthalpies of the bonds in the reactant is greater than the sum of the bond enthalpies of the bonds in the products b. the sum of the bond enthalpies of the bonds in the reactant is less than the sum of the bond enthalpies of the bonds in the products c. the length of the bond between carbon and oxygen in CH3OH is shorter than the length of the bond between carbon and oxygen in CO d. all of the bonds in the reactant and products are polar

a. the sum of the bond enthalpies of the bonds in the reactant is greater than the sum of the bond enthalpies of the bonds in the products

A 23.0g sample of a compound contains 12.0 g of C, 3.0g of H, and 8.0g of O. Which of the following is the empirical formula of the compound? a. CH3O b. C2H6O c. C3H9O2 d. C4H12O2

b. C2H6O

Based on the information in the table above, which liquid, CS2 (l) or CCl4 (l), has the higher equilibrium vapor pressure at 25 degrees C, and why? a. CS2 (l), because it has stronger London dispersion forces b. CS2 (l), because it has weaker London dispersion forces c. CCl4 (l), because it has stronger London dispersion forces d. CCl4 (l), because it has weaker London dispersion forces

b. CS2 (l), because it has weaker London dispersion forces

Which of the following Lewis electron-dot diagrams represents the molecule that contains the smallest bond angle? a. b. c. d.

b. NF3

2 NO2 (g) + F2 (g) -> 2 NO2F (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? a. F2 (g) -> 2 F (g) b. NO2 (g) + F2 (g) -> NO2F (g) + F (g) c. NO2 (g) + F (g) -> NO2F (g) d. 2 NO2 (g) + F2 (g) -> 2NO2F (g)

b. NO2 (g) + F2 (g) -> NO2F (g) + F (g)

Based on Coulomb's law and the information in the table above, which of the following cations is most likely to have the weakest interaction with an adjacent water molecule in an aqueous solution? a. Li+ b. Na+ c. Ca 2+ d. In 3+

b. Na+

At the point labeled R on the pH curve, which of the following ions are present in the reaction mixture at a concentration greater than 0.10 M? a. Na+ and Cl- only b. Na+, Cl-, and H+ only c. Na+, Cl-, and OH- only d. Na+, Cl-, H+, and OH-

b. Na+, Cl-, and H+ only

A student conducted an experiment to determine delta H rxn for the reaction between HCl (aq) and NaOH (aq). The student ran two trials using the volumes of HCl (aq) and NaOH (aq) indicated in the table above, and determined the amount of heat released. Which of the following best explains the relationship between X and Y? a. Y=2X, because the volume of HCl (aq) used in trial 2 is twice the volume used in trial 1 b. Y=X, because the number of moles of acid and base reacting with each other is the same in both trials c. Y=2X/3, because the heat is distributed over more particles in trial 2 and in trial 1 d. the relationship between X and Y cannot be predicted

b. Y=X, because the number of moles of acid and base reacting with each other is the same in both trials

C2H4 (g) + H2 (g) -> C2H6 (g) Which of the following will most likely increase the rate of the reaction represented above? a. decreasing the temperature of the reaction b. adding a heterogeneous catalyst to the reaction system c. increasing the volume of the reaction vessel using a piston d. removing some H2 (g) from the reaction system

b. adding a heterogeneous catalyst to the reaction system

At 1.0 atm a sample of ice is heated to liquid water and then to water vapor. The heating curve is shown in the graph above. Which of the following lists the signs for the changes in enthalpy and entropy for the process corresponding to segment X, going from left to right? a. delta H: positive // delta S: negative b. delta H: positive // delta S: negative c. delta H: negative // delta S: negative d. delta H: negative // delta S: positive

b. delta H: positive // delta S: negative

A mixture containing equal numbers of moles of ethyl acetate and butyl acetate was separated using distillation. Based on the diagrams shown above, which of the following identifies the substance that would be initially present in higher concentration in the distillate and correctly explains why that occurs? a. ethyl acetate, because it has fewer C-C bonds to break b. ethyl acetate, because it has a shorter carbon chain and weaker London dispersion forces c. butyl acetate, because it has more C-C bonds to break d. butyl acetate, because it has a longer carbon chain and weaker dipole-dipole attractions

b. ethyl acetate, because it has a shorter carbon chain and weaker London dispersion forces

What would be the effect on the reaction rate if the solution of C25H30N3+ (aq) is diluted by a factor of two? a. it would be higher b. it would be lower c. it would not change d. it would initially be higher but then rapidly decrease

b. it would be lower

O2 (g) + 2H+ (aq) +2 e- -> H2O2 (ag) What is the standard reduction potential for the half-reaction represented above? a. -1.78 V b. -0.68 V c. +0.68 V d. +1.78 V

c. +0.68 V

Approximately how long did it take for 75 percent of the initial amount of C25H30N3+ (aq) to react? a. 75 s b. 225 s c. 300 s d. 600 s

c. 300 s

To choose a wavelength to analyze the progress of the reaction, a student records the absorbance spectra of both C25H30N3+ (aq) and C25H30N3OH (aq) in the range of 200-800 nm. The two spectra are presented in the graph below. The student wants to use the spectrophotometer to measure [C25H30N3+] with the greatest sensitivity as the reaction progresses. Which of the following indicates the best wavelength setting and explains why it is best? a. 205 nm, because the colorless form of the molecule will absorb significantly at this wavelength b. 205 nm, because both forms of the molecule will absorb significantly at this wavelength c. 590 nm, because only the violet form of the molecule will absorb significantly at this wavelength d. 590 nm, because this wavelength falls in the violet region of the visible light spectrum

c. 590 nm, because only the violet form of the molecule will absorb significantly at this wavelength

Atoms of which element are reduced in the reaction? a. S; each atom loses four electrons b. Na in Na2O2; each atom loses one electron c. O in Na2O2; each atom gains one electron d. O in H2O; each atom gains one electron

c. O in Na2O2; each atom gains one electron

Based on the ionization energies of element X given in the table above, which of the following is most likely the empirical formula of an oxide of element X? a. XO2 b. X2O c. X2O3 d. X2O5

c. X2O3

A 2.0 mol sample of CO (g) and a 2.0 mol sample of H2O (g) are introduced into a previously evacuated 100. L rigid container, and the temperature is held constant as the reaction represented above reaches equilibrium. Which of the following is true at equilibrium? a. [H2O] > [CO] and [CO2] > [H2] b. [H2O] > [H2] c. [CO2] > [CO] d. [CO] = [H2O] = [CO2] = [H2]

c. [CO2] > [CO]

A student performs an acid-base titration and plots the experimental results in the graph above. Which of the following statements best explains the experimental findings? a. a strong acid was titrated with a strong base, as evidenced by the equivalence point at pH=7 b. a strong acid was titrated with a strong base, as evidenced by the equivalence point at pH >7 c. a weak acid was titrated with a strong base, as evidenced by the equivalence point at pH >7 d. a weak acid was titrated with a weak base, as evidenced by the equivalence point at pH approximately 7

c. a weak acid was titrated with a strong base, as evidenced by the equivalence point at pH >7

Which of the following is true for the decomposition of H2O2 (aq)? a. delta G >0 and Keq >1 b. delta G >0 and Keq <1 c. delta G <0 and Keq >1 d. delta G <0 and Keq <1

c. delta G <0 and Keq >1

At room temperature I2 (s) is a molecular solid. Which of the following provides a characteristic of I2 (s) with a correct explanation? a. it has a high melting point because it has weak intermolecular forces b. it is hard because it forms a three-dimensional covalent network c. it is not a good conductor of electricity because its valence electrons are localized in bonding and nonbonding pairs d. it is very soluble in water because its molecules are polar

c. it is not a good conductor of electricity because its valence electrons are localized in bonding and nonbonding pairs

Which of the following statements about the thermodynamic favorability of the reaction at 298 K is correct? a. it is thermodynamically unfavorable b. it is thermodynamically favorable and is driven by delta S only c. it is thermodynamically favorable and is driven by delta H only d. it is thermodynamically favorable and is driven by both delta H and delta S

c. it is thermodynamically favorable and is driven by delta H only

What can be inferred about delta S for the reaction at 600 K? a. it must be positive, since the reaction is thermodynamically unfavorable at 600 K b. it must be negative, since there are more moles of products than reactants c. it must be positive, since delta G is negative and delta H is positive d. it must be negative, since delta G is positive and delta H is positive

c. it must be positive, since delta G is negative and delta H is positive

Two trials are run, using excess water. In the first trial, 7.8g of Na2O2 (s) (molar mass 78 g/mol) is mixed with 3.2 g of S (s). In the second trial, 7.8g of Na2O2 (s) is mixed with 6.4g of S (s). The Na2O2 (s) and S (s) react as completely as possible. Both trials yield the same amount of SO2 (aq). Which of the following identifies the limiting reactant and the heat released, q, for the two trials at 298 K? a. limiting reactant: S // q: 30. kJ b. limiting reactant: S // q: 60 kJ c. limiting reactant: Na2O2 // q: 30. kJ d. limiting reactant: Na2O2 // q: 61 kJ

c. limiting reactant: Na2O2 // q: 30. kJ

A 1.0 L solution of AgNO3 (aq) and Pb(NO3)2 (aq) has a Ag+ concentration of 0.020 M and a Pb+ concentration of 0.0010 mol sample of K2SO4 (s) is added to the solution. Based on the information in the table above, which of the following will occur? (Assume that the volume change of the solution is negligible). a. No precipitate will form b. only Ag2SO4 (s) will precipitate c. only PbSO4(s) will precipitate d. both Ag2SO4(s) and PbSO4 (s) will precipitate

c. only PbSO4(s) will precipitate

For element X represented above, which of the following is most likely explanation for the large difference between the second and third ionization energies? a. the effective nuclear charge decreases with successive ionizations b. the shielding of outer electrons increases with successive ionizaitons c. the electron removed during the third ionization is, on average, much closer to the nucleus that the first two electrons removed were d. the ionic radius increases with successive ionization

c. the electron removed during the third ionization is, on average, much closer to the nucleus that the first two electrons removed were

One student titrated the NaOH (aq) with 1.0 M HCl (aq) instead of 0.10 M HCl (aq). How would the student's titration curve differ from the original curve? a. the initial pH would be 11 instead of 13 b. the pH at the equivalence point would be 5 instead of 7 c. the pH far beyond the equivalence point would be higher than in the original curve d. the pH far beyond the equivalence point would be lower than in the original curve

c. the pH far beyond the equivalence point would be higher than in the original curve

Two samples of Mg (s) of equal mass were placed in equal amounts of HCl (aq) contained in two separate reaction vessels. Particle representations of the mixing of Mg (s) and HCl (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? a. the reaction in Figure 1, because the atoms of Mg are more concentrated than those in Figure 2 b. the reaction in Figure 1, because the Mg (s) in Figure 1 has a larger mass than the Mg (s) in Figure 2 c. the reaction in Figure 2, because more Mg atoms are exposed to HCl (aq) in Figure 2 than in Figure 1 d. the reaction in Figure 2, because the Mg (s) in Figure 2 has less surface area than the Mg (s) in Figure 1

c. the reaction in Figure 2, because more Mg atoms are exposed to HCl (aq) in Figure 2 than in Figure 1

What happens to the temperature of the contents of the vessel as the reaction occurs? a. the temperature must increase, because according to Le Chatelier's principle, an increase in temperature cause more products to form b. the temperature must decrease, because the reaction takes place at a temperature above room temperature c. the temperature must decrease, because the reaction is endothermic d. the temperature does not change, because the vessel is insulated

c. the temperature must decrease, because the reaction is endothermic

Fe (s) + 2HCl (aq) -> FeCl2 (aq) + H2 (g) When a student adds 30.0 mL of 1.00 M HCl to 0.56 g of powedered Fe, a reaction occurs according to the equation above. When the reaction is complete at 273 K and 1.0 atm, which of the following is true? a. HCl is in excess, and 0.100 mol of HCl remains unreacted b. HCl is in excess, and 0.020 mol of HCl remains unreacted c. 0.015 mol of FeCl2 has been produced d. 0.22 L of H2 has been produced

d. 0.22 L of H2 has been produced

In which of the following liquids do the intermolecular forces include dipole-dipole forces? a. F2(l( b. CH4 (l) c. CF4 (l) d. CH2F2 (l)

d. CH2F2 (l)

The photoelectron spectra of the Is electrons of two isoelectronic species, Ca2+ and Ar, are shown above. Which of the following correctly identifies the species associated with peak X and provides a valid justification? a. Ar, because it has completely filled energy levels b. Ar, because its radius is smaller than the radius of Ca2+ c. Ca2+, because its nuclear mass is greater than that of Ar d. Ca2+, because its nucleus has two more protons than the nucleus of Ar has

d. Ca2+, because its nucleus has two more protons than the nucleus of Ar has

Based on the information above and periodic trends, which of the following is the best hypothesis regarding the oxide (s) formed by Rb? a. Rb will form only Rb2O b. Rb will only form only RbO2 c. Rb will form only Rb2O and Rb2O2 d. Rb will form Rb2O, Rb2O2, and RbO2

d. Rb will form Rb2O, Rb2O2, and RbO2

Which of the following correctly ranks the three monoprotic acids listed in the table above from the weakest to the strongest? a. X < Y < Z b. X < Z < Y c. Y < Z < X d. Z < Y < X

d. Z < Y < X

NH3 (g) was synthesized at 200 degrees C in the presence of a powdered Os (s) catalyst, leading to the equilibrium system represented above. Which of the following changes would result in more NH3 (g) in the mixture after equilibrium is reestablished? a. replacing the powdered Os (s) with a solid cube of Os (s) of the same total mass b. increasing the temperature of the system to 250 degrees C at constant pressure c. removing some H2 (g) d. adding some N2 (g)

d. adding some N2 (g)

Which of the following best helps explain why an increase in temperature increases the rate of a chemical reaction? a. at higher temperatures, reactions have a lower activation energy b. at higher temperatures, reactions have a higher activation energy c. at higher temperatures, every collision results in the formation of product d. at higher temperatures, high-energy collisions happen more frequently

d. at higher temperatures, high-energy collisions happen more frequently

A vessel contains Ar (g) at a high pressure. Which of the following statements best helps to explain why the measured pressure is significantly greater than the pressure calculated using the ideal gas law? a. the molar mass of Ar is relatively large b. a significant number of Ar2 molecules form c. the attractive forces among Ar atoms cause them to collide with the walls of the container with less force d. the combined volume of the Ar atoms is too large to be negligible compared with the total volume of the container

d. the combined volume of the Ar atoms is too large to be negligible compared with the total volume of the container

A student performed an analysis to determine the amount of AgNO3 (aq) in a solution. Excess NaCl (aq) was added to the solution, and the Ag+ (aq) precipitated as AgCl (s). The precipitate was collected by gravity filtration and dried in an oven. Three trials were performed, and in each case, according to the instructor, the mass of precipitate recovered was 5 percent higher than the actual mass of AgCl (s) that should have formed. Which of the following could account for the error? a. the pores in the filter paper were too large b. not all of the precipitate was transferred to the filter paper c. the NaCl (aq) solution was too concentrated d. the precipitate was not rinsed with deionized water before drying

d. the precipitate was not rinsed with deionized water before drying

Which of the following molecules is least soluble in water? a. b. c. d.

b. CCl4

The pH of a 0.01 M HNO2 (aq) solution is in which of the following ranges? (For HNO2 (aq), Ka= 4.0 x 10^-4) a. between 1 and 2 b. between 2 and 3 c. between 4 and 5 d. between 6 and 7

b. between 2 and 3

A sample of CH3OH (g) is placed in the previously evacuated vessel with a pressure of P1 at 600 K. What is the final pressure in the vessel after the reaction is complete and the contents of the vessel are returned to 600 K? a. P1/9 b. P1/3 c. P1 d. 3P1

d. 3P1

The distribution of speeds of H2 (g) molecules at 273 K and 1 atm is shown in the diagram above. Which of the following best shows the speed distribution of He (g) atoms under the same conditions of temperature and pressure a. b. c d.

a.