AP Chemistry 2014

39. How much energy is required to melt 64g of methane at 90K? (The molar mass of methane is 16g/mol.)

B. 3.8kJ

38. Data collected during the titration of a 20.0mL sample of a 0.10M solution of a monoprotic acid with a solution of NaOH of unknown concentration are plotted in the graph above. Based on the data, which of the following are the approximate pHa of the acid and the molar concentration of the NaOH?

B. 4.7, 0.10M

45. Which of the following best describes the flow of the heat when 1.0 mol of XY2 decomposes?

B. 50kJ of heat is transferred from the surroundings.

37. Consider the reaction represented above at 298K. When equal volumes of N2(g) and H2(g), each at 1 atm, are mixed in a closed container at 298K, no formation of NH3(g) is observed. Which of the following best explains the observation.

B. A high activation energy makes the forward reaction extremely slow at 298K.

41. The enthalpy of vaporization of water is 40.7kJ/mol. Which of the following best explains why the enthalpy of vaporization of methane is less than that of water?

A. Methane does not exhibit hydrogen bonding but water does.

10. Which of the following diagrams best represents the AgNO3 solution before the reaction occurs?

A.

47. Which of the following diagrams best illustrates how a displacement in an ionic crystal results in cleavage and brittleness?

A.

11. When 200. mL of 2.0M NaOH(aq) is added to 500. mL of 1.0M HCl(aq), the pH of the resulting mixture is closest to

A. 1.0

14. On the basis of the data provided above, the gas in container 3 could be

A. CH4

17. The potential energy as a function of the internuclear distance for three diatomic molecules, X2, Y2, and Z2, is shown in the graph above. Based on the data in the graph, which of the following correctly identifies the diatomic molecules, X2, Y2, and Z2?

A. H2, N2, O2

40. Which of the following best explains why more energy is required for the process occurring at 110L than for the process occurring at 90K?

A. Intermolecular attractions are completely overcome during vaporization.

26. In the reaction represented above, the number of MnO4- ions that react must be equal to which of the following?

A. One-fifth the number of Fe2+ ions that are consumed

33. Which element is being oxidized during the titration, and what is the element's change in oxidation number?

A. Oxygen, which changes from -1 to 0

18. A 10. g cube of coiner at a temperature T1 is placed in an insulated cup containing 10. g of water at a temperature T2. If T1 > T2, which of the following is true of the system when it has attained thermal equilibrium? (The specific heat of copper is 0.385J/(g.°C) and the specific heat of water is 4.18J/(g.°C).)

A. The temperature of the copper changed more than the temperature of the water.

15. Under the conditions given, consider containers 1, 2, and 4 only. The average speed of the gas particles is

A. greatest in container 1

42. a sample of steel-chromium alloy contains 15 percent Cr by mass. Which of the following diagrams best shows a particle-level view of a surface section and an interior section of the allow represented below at the left? (The atomic radii of the atoms involved are given in the table below at the right.)

B.

49. The table above shows the structural formulas and molar masses for three different compounds. Which of the following is a list of the compounds in order of increasing boiling points?

B. Butane < acetone < 1-propanol

23. A mixture of CO(g) and H2(g) is pumped into a previously evacuated 2.0L reaction vessel. The total pressure of the system if the volume of the reaction vessel is reduced to 1.0L at constant temperature?

B. Greater than 1.2 atm but less than 2.4 atm

8. What is the identity of the metal chloride?

B. KCl

1. According to the information in the table above, a 1.00g sample of which of the following contains the greatest mass of oxygen?

B. MgO

2. Which of the following could be the identity of a white crystalline solid that exhibits the following properties? - It melts at 320 °C - It does not conduct electricity as a solid -It conducts electricity in an aqueous solution

B. NaOH (s)

31. A sample containing atoms of C and F was analysed using x-ray photoelectron spectroscopy. The portion of the spectrum showing the 1s peaks for atoms fo the two elements is shown above. Which of the following correctly identifies the 1s peak for the F atoms and provides an appropriate explanation?

B. Peak X, because F has a greater nuclear charge than C has.

50. 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?

B. The two reactant particles must collide with a particular orientation in order to react.

22. A 1.0 mol sample of CO(g) and a 1.0 mol sample of H2(g) are pumped into a rigid, previously evacuated 2.0L reaction vessel at 483K. Which of the following is true at equilibrium?

B. [H2] < [CO]

43. Consider the reaction represented by the equation 2X + 2Z -> 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

B. first order

29. On the basis of the information above, the dissolution of FeF2(s) in acidic solution is

B. thermodynamically favourable, because K1 < 1

48. A 6.0mol sample of C3H8(g) and a 20. mol sample of Cl2(g) are placed in a previously evacuated vessel, where they react according to the equation above. After one of the reactants has been totally consumed, how many moles of HCl(g) have been produced?

C. 20. mol

6. Under which of the following conditions of temperature and pressure will H2 gas be expected to behave most like an ideal gas?

C. 500K and 50atm

34. Which of the following best describes what happens to the pH of the H2O2 solution as the titration proceeds?

C. As H+ ions are consumed, the solution becomes less acidic and the pH increases.

28. 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>

C. Both mechanism 1 and mechanism 2 are consistent with the rate law.

5. Which of the following best helps to explain why the value of ΔH° for the dissolving of CaF2 in water is positive?

C. Ca2+ ions have very strong ion-ion interactions with F- ions in the crystal lattice

13. Which of the following equations represents a reaction for which the standard entropy change is positive (ΔS° > 0)?

C. CaCo3(s) -> CaO(s) + CO2(g)

19. A solution containing HCl and the weak acid HClO2 has a pH of 2.4. Enough KOH(aq) is added to the solution to increase the pH to 10.5. The amount of which of the following species increases as the KOH(aq) is added?

C. ClO2-(aq)

25. A solution is prepared by adding 100mL of 1.0M HC2H3O2(aq) to 100mL of 1.0M NaC2H3O2(aq). The solution is stirred and its pH is measured to be 4.73. After 3 drops of 1.0M HCl are added to the solution, the pH of the solution is measured and is still 4.73. Which of the following equations represents the chemical reaction that accounts for the fact that acid was added but there was no detectable change in pH?

C. H3O+(aq) + C2H3O2(aq) -> HC2H3O2(g) + H2O(l)

21. Which of the following explains the effect on the equilibrium constant, Kc, when the temperature of the reaction system is increased to 650K?

C. Kc will decrease because the reaction is exothermic.

7. The volume of a sample of air in a cylinder with a movable piston is 2.0L at a pressure P1, as shown in the diagram above. The volumes increased to 5.0L as the temperature is held constant. The pressure of the air in the cylinder is now P2. What effect do the volume and pressure changes have on the average kinetic energy of the molecules in the sample?

C. The average kinetic energy stays the same.

24. Which of the following statements is true about bond energies in this reaction?

C. The energy absorbed as the bonds in the reactants are broken is less than the energy released as the bonds in the product are formed.

36. At a certain point in time, a 1.00L rigid reaction vessel contains 1.5 mol of PCl5(g). Which of the following describes how the measured pressure in the reaction vessel will change and why it will change that way as the reaction system approaches equilibrium at constant temperature?

C. The pressure will decrease because Q < Kc.

12. The table above shows the first ionization energy and atomic radius of several elements. Which of the following best helps to explain the deviation of the first ionisation energy of oxygen from the overall trend?

C. There is repulsion between paired electrons in oxygen's 2p orbitals.

46. The reaction is thermodynamically favorable under standard conditions at 298K. Therefore, the value of ΔS° for the reaction must be

C. greater than ΔH°/298K

16. The best explanation for the lower pressure in container 4 is that SO2 molecules

C. have stronger intermolecular attractions than the other three gases

30. Thymine and adenine form a base pair in the DNA molecule. These two bases can form a connection between two strands of DNA via two hydrogen bonds. Which of the following diagrams shows the correct representation of the hydrogen bonding (denoted by dashed lines) between thymine and adenine base pairs? (In each diagram, thymine is shown at the left and adenine shown at the right. The bases are attached to the backbone portion of the DNA strands.)

D.

32. At a certain time during the titration, the rate of appearance O2(g) was 1.0 x 10^-3 mol/(L x s). What was the rate of disappearance of MnO40 at the same time?

D. 4.0 x 10^-4 mol/(L x s)

3. Which of the following correctly identifies which has the higher first-first-ionization energy, Cl or Ar, and supplies the best justification?

D. Ar because of its higher effective nuclear charge

20. The autoionization of water is represented by the equation above. Values of pKw at various temperatures are listed in the table below. Based on the information above, which of the following statements is true?

D. As the temperature increases, the pH of pure water decreases.

4. A sealed rigid vessel contains BaO2 (s) in equilibrium with BaO2 (s) and O2 (g) as represented by the equation above. Which of the following changes will increase the amount of BaO2 (s) in the vessel?

D. Lowering the temperature

27. A student prepared five solutions of CuSO4 with different concentrations, and then filled five cuvettes, each containing one of the solutions. The cuvettes were placed in a spectrophotometer set to the appropriate wavelength for maximum absorbance. The absorbance of each solution was measured and recorded. The student plotted absorbance versus concentration, as shown in the figure above. Which of the following is the most likely explanation for the variance of the data point for the 0.600M CuSO4 solution?

D. The cuvette used for the 0.600M solution had not been wiped clean before being put in the spectrophotometer.

44. Which of the following most likely accounts for the difference between reaction path one and reaction path two?

D. The presence of a catalyst in path two.

9. During the course of the experiment, which of the following happens to the NO3- ions?

D. They remain dissolved in the filtrate solution.

35. The BF3 molecule is non polar, whereas the NF3 molecule is polar. Which of the following statements accounts for the difference in polarity of the two molecules?

D. Unlike BF3, NF3 has a non polar geometry due to an unshared pair of electrons on the N atom.