AP Chemistry MCQ

Which of the following best describes the change that takes place immediately after the CH3OH(l) is introduced into the previously evacuated vessel?

A physical change takes place because intermolecular attractions are overcome

Which of the following Lewis electron-dot diagrams represents the molecule is the most polar?

B (Br-F)

When H2 and O2 are mixed together in a rigid reaction vessel at 25 C, no reaction occurs. When the mixture is sparked, however, the gases react vigorously according to the equation above, releasing heat. Which of the following statements correctly explains why the spark is needed for the reaction to occur when the gasses are originally at 25C?

The reaction has a large activation energy at 25 C

Compared to the equilibrium vapor pressure of CH3OH at 300 K, the equilibrium vapor pressure of C2H5OH at 300 K is

lower, because LDFs among C2H5OH molecules are greater than those among the CH3OH

What is the value of the enthalpy change per mole of HCl produced?

-93 kJ

The temperature of the CH3OH is increased from 300 K to 400 K to vaporize all the liquid, which increases the pressure in the vessel to 0.30 atm. The experiment is repeated under identical conditions but this time using half the mass of CH3OH that was originally used. What will the pressure be in the vessel at 400 K?

0.15 atm

The value of Kp for the evaporation of CH3OH at 300 K is closest to

0.2

The students determined that the reaction produced .01 mol of CuNO3. Based on the measurement, what was the percent of Cu by mass in the original 2.00 g sample of the mixture? 16% 32% 64% 96%

32%

The reactions represented above are carried out in sealed, rigid containers and allowed to reach equilibrium. If the volume of each container is reduced from 1.0 L to 0.5L at constant temperature, for which of the reactions will the amount of product(s) be increased?

A

When a small amount of 12M HNO3 is added to a buffer solution made by mixing CH3NH2 and CH3NH3Cl, the pH of the buffer solution changes from 10.64 to 10.62. Which of the following equations represents the reaction that accounts for the fact that the pH does not change significantly when the HNO3 is added?

A

Dissolution of the slightly soluble salt CaF2 is shown by the equation above. Which of the following changes will decrease [Ca2+] in a saturated solution of CaF2, and why?

Adding NaF(s), because the reaction will proceed to the reactants

The first ionization energy of an element is the energy required to remove an electron from a gaseous atom of the element. The values of the first ionization energies for the third-row elements are shown in the graph above. On the basis of the information given, which of the following reactions is exothermic?

Al(g) + Mg+(g) --> Al+(g) + Mg(g)

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

B

Based on the information in the table above, which of the following shows the cell potential and the Gibbs free energy change for the overall reaction that occurs in a standard galvanic cell?

B (+1.63,-944)

A student prepares a soution by combining 100 mL of 0.30 M HNO2 and 100 mL pf 0.30 M KNO3. Which of the following equations represents the reaction that best helps to explain why adding a few drops of 1.0 M HCl does not significantly change the pH of the solution?

D

NH3 reacts with BF3 to form a single species. Which of the following structural diagrams is the most likely representation of the product of the reaction?

D

Which of the substances listed above has the highest boiling point, and why?

HF, because its molecules form hydrogen bonds

Equimolar samples of Pb(OH)2m PbI2, and PbF2 are placed in three seperate beakers, each containing 250 mL of water at 25 C. After the solutions are stirred, solid remains at the bottom of the beaker. Based on the Ksp values for the compounds listed above, a solution of which of the following compounds will have the lowest [Pb2+]

Pb(OH)2

The step-wise dissociation of selenious acid is represented by the equations above. Which of the following best helps explain why the value of Ka2 is so much smaller than Ka1?

Removing the first H+ from H2SeO3(aq) requires less energy than removing the second H+, because the second H+ is removed from a negatively charged species.

Based on Coulomb's Law and the information in the table above, which of the following anions is most likely to have the strongest interactions with nearby water molecules in an aqueous solution?

S2-

If a pure sample of an oxide of sulfur contains 40 percent sulfur and 60 percent oxygen by mass, then the empirical formula of the oxide is

SO3

The mass of the Cu(s) produced in step 3 was slightly more than the mass predicted from the 3.8 g Cu3(PO4)2 recovered from step 1. Which of the following could account for the discrepancy in the yield of Cu from step 3?

Some unreacted Zn was mixed in with the Cu

The table above provides some information about two types of steel, both of which are alloys of iron and carbon. Which of the following best helps to explain why high-carbon steel is more rigid than low-carbon steel?

The additional carob atoms within the alloy make it more difficult for the iron atoms to slide past one another

For the system represented above, [O2] and [O3] initially are 0.150 mol/L and 2.5 mol/L respectively. Which of the following best predicts what will occur as the system approaches equilibrium at 570 K?

The amount of O3 will decrease because Q > Kc

Which of the following statements best helps to explain why the contents of the tube containing the equilibrium mixture turned a lighter color when the tube was placed into an ice bath?

The forward reaction is endothermic

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

The equilibrium system represented by the equation above initially contains equal concentrations of Cr2O72- and CrO42-. Which of the following statements correctly predicts the result of adding a sample of 6.0 M NaOH to the system and provides an explanation?

The mixture will become more yellow because OH- will shift the equilibrium toward products

The ionization energies of an unknown element, X, are listed in the table above. Which of the following is the most likely empirical formula of a compound formed from element X and phosphorus, P?

X3P2

The mass spectrum of an average sample of a pure element is shown in the figure above. Which of the following is the identity of the element?

Zr

Which of the following statements about delta H for the reaction is correct?

Delta H > 0 becuase energy is required to break the N-N bond

Which of the following has the bonds arranged in the order of decreasing polarity?

H-F > N-F > F-F

Based on the information in the table above, which of the compounds has the highest boiling point, and why?

Propanoic acid, because it can form intermolecular hydrogen bonds

Which of the following correctly compares periodic properties of two elements and provides an accurate explanation for that difference?

The atomic radius of Cl is smaller than that of S because Cl has a larger nuclear charge than S does

A sample of a solid labeled as NaCl may be impure. a student analyzes the sample and determines that it contains 75 percent chlorine by mass. Pure NaCl contains 61 percent chlorine by mass. Which of the following statements is consistent with the data?

The sample contains NaCl(s) and LiCl(s)