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MCAT Warm-up

1 .       Passage I (Questions 1-8)

Under standard conditions, how many of the substances listed in the table can be formed spontaneously from their constituent elements? 

2 .       Passage I (Questions 1-8)

Using the values in the table, what is S°(in J/mol K) for the following reaction?

2H2(g) + O2(g) --> 2H2O(g)

3 .       Passage I (Questions 1-8)

According to the table, the amount of heat needed, at constant pressure, to raise the temperature of 10 g of gaseous carbon 10K would raise the temperature of the same mass of graphite by how many degrees? 

4 .       Passage I (Questions 1-8)

For the data shown in the table, the molar heat capacities of saturated hydrocarbons: 

5 .       Passage I (Questions 1-8)

The value of Hf° for C2H2 is considerably higher than that for C2H4. The heat capacities for the two compounds are very similar. Therefore, which of the following is (are) likely to be true?

I. The energy of a double bond differs substantially from that of a triple bond.

II. When heat is added to each of these compounds at 298K, more of the heat will be absorbed by the triple bond than by the double bond.

III. When each compound is decomposed into its elements at their standard states, more energy is released by C2H2

6 .       Passage I (Questions 1-8)

Among the halogenated hydrocarbons shown in the table, which of the following increases as the number of chlorines increases? 

7 .       Passage I (Questions 1-8)

The free energy change (in kJ) when 2 moles of C2H6 are oxidized to CO2 and H2O is approximately which of the following? 

8 .       Passage I (Questions 1-8)

Which of the following expressions can be used to calculate the equilibrium constant for the following reaction?

CO(g) + 1/2 O2(g) --> CO2(g)

9 .       Passage II (Questions 9-15)

Which of the following expresses the ratio of average speeds of a molecule of O2 to a molecule of H2 when both are at the same temperature? 

10 .       Passage II (Questions 9-15)

If the temperature of a mole of gaseous O2 is raised from 100oC to 200oC, the average speed of the molecules is: 

11 .       Passage II (Questions 9-15)

Based on the graph, the most probable speed at 600K is closest to which of the following? 

12 .       Passage II (Questions 9-15)

Based on the graph, for 600K, what is the approximate fraction of molecules having speeds greater than 1,600 m/s? 

13 .       Passage II (Questions 9-15)

Based on the graph, the curve for 1,200K is most likely to peak at which of the following? 

14 .       Passage II (Questions 9-15)

The fact that there are no negative speeds on the graph reflects: 

15 .       Passage II (Questions 9-15)

Which of the following may be inferred from the speed distributions shown on the graph?

I. At higher temperatures, the average speed is higher.

II. At lower temperatures, the speed distribution is more widely distributed.

III. The average speed is proportional to the absolute temperature. 

16 .       Passage III (Questions 16-24)

Which of the following is the number of moles of NaOH added at the endpoint of the titration shown in the graph? 

17 .       Passage III (Questions 16-24)

The data in the graph indicate that the concentration of the unknown acid is which of the following? 

18 .       Passage III (Questions 16-24)

In the titration shown in the graph, as the volume of NaOH added is changed from 8 to 30 mL, the change in [H+] is approximately: 

19 .       Passage III (Questions 16-24)

Based on the graph, the ratio V OH-/pH is smallest when VOH- equals: 

20 .       Passage III (Questions 16-24)

Based on the information given, what is the pH when VOH- = 100 mL? 

21 .       Passage III (Questions 16-24)

Based on the data in the table and the titration curve shown in the graph, which of the following is the unknown acid? 

22 .       Passage III (Questions 16-24)

A second sample of the unknown acid is titrated with NaOH of the same concentration, and the endpoint is found to occur at 60 mL. The solution is then titrated with 30 mL of 0.20 M HCl. The resulting pH is closest to which of the following? 

23 .       Passage III (Questions 16-24)

At the 40-mL point on the graph, the solution most closely resembles which of the following mixtures (where "conjugate acid/base" refers to the unknown acid)? 

24 .       Passage III (Questions 16-24)

The student wishes to choose an indicator to signal the equivalence point of the titration. Indicators that change color at pH 7.5 or 8.5 are available. Which should she choose? 

25 .       Passage IV (Questions 25-28)

Of the reactions for which H is given, how many can be said with certainty to proceed spontaneously? 

26 .       Passage IV (Questions 25-28)

Find the energy taken in or given off when 20 moles of gaseous chlorine atoms are converted to gaseous Cl2 molecules. 

27 .       Passage IV (Questions 25-28)

Using the results of the experiments, what energy would be necessary to produce 0.10 mol of gas-phase silver ion (Ag+) from metallic silver? 

28 .       Passage IV (Questions 25-28)

Find the heat added or given off when 0.5 mol AgCl(s) is converted to gaseous Ag atoms and gaseous Cl atoms. 

29 .       Passage V (Questions 29-32)

In Figure 1, which point corresponds to a pressure and temperature at which sublimation is taking place? 

30 .       Passage V (Questions 29-32)

Consider Figures 1 and 2. Which would best describe water, given that water has the unusual property of expanding as it freezes 

31 .       Passage V (Questions 29-32)

Referring to Figure 3, determine the phase that will exist in a mixture of aluminum and 1.00% silicon at 550oC. 

32 .       Passage V (Questions 29-32)

Which of the following statements may be inferred from the diagram?

According to the diagram, as the percentage of silicon increases:

I. The minimum temperature needed for the existence of any solid decreases.

II. The maximum temperature at which solid 2 appears increases sharply, then levels out.

III. The minimum temperature at which liquid is found decreases at a roughly constant rate. 

33 .       Passage VI (Questions 33-41)

How many of the reactions in the table are spontaneous? 

34 .       Passage VI (Questions 33-41)

An investigator who wishes to test the hypothesis that the entropy change is positive for a reaction that results in more product molecules or ions than reactants would find what pattern in the data? 

35 .       Passage VI (Questions 33-41)

An investigator wishing to predict the direction of entropy change as dry ice (solid CO2) sublimes to its vapor would get the best prediction from which of the following reactions? 

36 .       Passage VI (Questions 33-41)

Given the value S° for reaction 3 and the high solubility of NaCl in water, it can be said that the enthalpy change of NaCl solution: 

37 .       Passage VI (Questions 33-41)

The S for a phase change equals the enthalpy change for the phase change divided by the temperature at the phase change. In order to predict the melting point of ice, an investigator would need to know: 

38 .       Passage VI (Questions 33-41)

In order to explain the difference between the S° values given for the two forms of carbon, an investigator might reasonably suggest which of the following?

I. A mole of diamond consists of fewer particles than a mole of graphite.

II. Diamond is a more stable structure than graphite.

III. The structure of diamond is more ordered than that of graphite. 

39 .       Passage VI (Questions 33-41)

An investigator wishes to account for the difference in S° between NaCl and MgCl2. Which of the following would NOT help to explain the difference?

I. Entropy changes increase as the number of product molecules increase.

II. When Mg2+ is dissolved, its large positive charge causes a more orderly arrangement of water molecules around it than in the case of Na+.

III. The heat of solution is greater for MgCl2 than for NaCl. 

40 .       Passage VI (Questions 33-41)

What is the maximum number of electrons in an atom that can have quantum numbers of n = 5 = l = 2? 

41 .       Passage VI (Questions 33-41)

Which of the following are arranged in decreasing order of expected dipole moment? 

42 .       The solubility product for BaSO4 is 1.5 x 10-9. Which of the following is correct?

I. The solubility of BaSO4 in pure water is greater than the solubility in 0.1 M Ba(NO3)2.

II. The solubility product of BaSO4 in pure water is greater than the solubility product in 0.1 M Ba(NO3)2.

III. The reaction of Ba2+ with SOhas an equilibrium constant greater than 1.0. 

43 .       A student finds that MgCO3 is more soluble in HNO3 than in plain water. Which of the following is a likely explanation for this effect? 

44 .       For the reaction E + 2F --> G, it is found that doubling the concentration of E quadruples the rate, while doubling the concentration of F has no effect. The rate law is which of the following? 

45 .       An electron in a pz orbital is least likely to be found: 

46 .       The pH of a solution of 0.1 M HNO3 is closest to which of the following? 

47 .       A gas mixture containing 1 mole of H2 and 3 moles of N2 has a total pressure of P atm. Which of the following are the partial pressures of each gas? 

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