Thermodynamics - 5 STEPS TO A 5: 500 AP Chemistry Questions to Know by Test Day! (2012)

5 STEPS TO A 5: 500 AP Chemistry Questions to Know by Test Day! (2012)

Chapter 6. Thermodynamics (Questions 231–269)

Questions 231–237 refer to the following answer choices:

(A) Activation energy

(B) Lattice energy

(C) Free energy

(D) Kinetic energy

(E) Potential energy

231. The energy needed to convert an ionic solid into well-separated gaseous ions

232. The energy liberated from a physical or chemical process that is available to do work

233. The energy needed for the formation of the transition state of a chemical reaction

234. The energy needed to overcome the activation barrier of a chemical reaction

235. This quantity is determined by measuring the rate of a particular reaction at two or more different temperatures

236. This quantity must change in any substance undergoing a phase change

237. The formula for this quantity is used to derive the effusion ratio of O2 and CO2 at the given temperature

Questions 238–241 refer to the following answer choices:

(A) Enthalpy of formation

(B) Entropy

(C) Energy of crystallization

(D) Activation energy

(E) Gibbs free energy

238. A quantity that is zero for a perfect, pure crystalline solid at 0 K

239. A quantity that is zero when a reaction is at equilibrium at constant temperature and pressure

240. A quantity that is zero for a pure element in its standard state

241. A quantity that describes a feature of a chemical reaction and is always positive for reactions in which an increase in temperature results in an increased reaction rate

Questions 242–247 refer to the following answer choices:

(A) ΔH > 0, ΔS > 0

(B) ΔH < 0, ΔS < 0

(C) ΔH > 0, ΔS < 0

(D) ΔH < 0, ΔS > 0

(E) ΔH = 0, ΔS > 0

242. Must be true for a reaction that is spontaneous at all temperatures

243. True for melting of water at 25°C and 1 atm

244. True for the deposition of CO2(g) into CO2(s) at –100°C and 1 atm

245. True for the combustion of wood into CO2(g) and H2O(g) in a campfire

246. Must be true for a reaction that is never spontaneous at any temperature

247. True for the mixing of two ideal gases (no intermolecular forces of attraction or repulsion occur between any of the gas particles) at a constant temperature and pressure. Assume no reaction occurs.

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248. The decomposition of CaCO3(s) is shown in the equation above. Using the data in the table above the reaction, which of the following values is closest to the ΔHrxn of the decomposition of CaCO3(s)?

(A) −2,240 kJ mol−1

(B) −180 kJ mol−1

(C) 180 kJ mol−1

(D) 1,207 kJ mol−1

(E) 2,240 kJ mol−1

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249. The reactions for the combustion of diamond and graphite are shown above. Which of the following values is closest to the ΔHrxn for the conversion of C(graphite) to C(diamond)?

(A) −789 kJ

(B) −1.9 kJ

(C) 1.9 kJ

(D) 394.45 kJ

(E) 798 kJ

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250. The entropy change for the dissolution of calcium chloride in water shown above might be expected to be positive, but the actual ΔS is negative. Which of the following is the most plausible explanation for the net loss of entropy during this process?

(A) CaCl2(s) is an amorphous solid.

(B) The particles in the solution are more ordered than the particles in the solid.

(C) The ions in solution can move more freely than the particles in the solid.

(D) The decreased entropy of the water molecules in the solution is greater than the increased entropy of the ions.

(E) In solution, the distance between ions is much greater than the distance between the ions in the solid.

251. Which of the following best describes the role of a spark in a butane lighter?

(A) The spark decreases the activation energy of the combustion reaction.

(B) The spark increases the concentration of butane in the reaction chamber.

(C) The spark provides the heat of vaporization for the liquid fuel.

(D) The spark supplies some of the energy to form the activated complex for the combustion reaction.

(E) The spark provides an alternative stoichiometry for the reaction, decreasing the amount of oxygen required for complete combustion.

252. Which of the following processes demonstrates a decrease in entropy (ΔS < 0)?

(A) Br(s) → Br(l)

(B) I2(s) → I2(g)

(C) Combining equal volumes of C2H6O2(l) and H2O(l)

(D) The precipitation of PbI2 from solution

(E) The thermal expansion of a helium balloon

253. Which of the following reactions involves the largest decrease in entropy?

(A) MgCO3(s) → MgO(s) + CO2(g)

(B) 3 H2(g) + N2(g) → 2 NH3(g)

(C) 4 La(s) + 3 O2(g) → 2 La2O3(s)

(D) 2 NaI(aq) + Pb(CH3COO)2(aq) → 2 NaCH3COO(aq) + PbI2(s)

(E) C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g)

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254. The combustion of methylhydrazine, a common rocket fuel, is represented above. The ΔH of this reaction is –1,303 kJ mol−1CH6N2(l). What would be the ΔH per mol CH6N2(l) if the reaction produced H2O(l) instead of H2O(g)? (The ΔH for the condensation of H2O(g) to H2O(l) is –44 kJ mol−1.)

(A) –1,171 kJ

(B) –1,259 kJ

(C) –1,347 kJ

(D) –1,567 kJ

(E) –1,435 kJ

255. A student adds solid ammonium chloride to a beaker containing water at 25°C. As it dissolves, the beaker feels colder. Which of the following are true regarding the ΔH and ΔS of the dissolution process of NH4Cl(s)?

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256. Suppose a reaction is spontaneous at temperatures only below 300 K. If the ΔHa° for this reaction is –18.0 kJ mol−1, the value of ΔS° for this reaction is closest to which of the following? Assume ΔS° and ΔH° do not change significantly with temperature.

(A) –60 J mol−1K−1

(B) –18 J mol−1K−1

(C) –0.0010 J mol−1K−1

(D) 18 J mol−1K−1

(E) 18,000 J mol−1K−1

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257. The normal melting point of Ag(s) is 962°C. Which of the following is true for the process represented above at 962°C?

(A) ΔH = 0

(B) ΔS = 0

(C) TΔS = 0

(D) ΔH = TΔS

(E) ΔH > TΔS

258. The standard Gibbs free energy change, ΔG°298, for the conversion of Cdiamond into Cgraphite has an approximate value of –3 kJ mol−1. However, graphite does not form from diamond under standard conditions (298 K and 1 atm). Which of the following best explains this observation?

(A) Diamond is more ordered than graphite (lower entropy).

(B) The ΔH for the conversion of diamond to graphite is highly endothermic.

(C) The activation energy for the conversion of diamond to graphite is very large.

(D) The C–C bonds in diamond are much stronger than the C–C bonds in graphite.

(E) Diamond is significantly denser than graphite.

259. Which of the following is true regarding the adiabatic and reversible compression of an ideal gas?

(A) The temperature of the gas remains constant.

(B) The volume of the gas remains constant.

(C) The pressure of the gas remains constant.

(D) No work can be done by the gas.

(E) The net entropy change of the gas is zero.

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260. Given the bond energies in the table above, which of the following statements best describes the formation of 1 mole of H2O(l) from H2(g) and O2(g)?

(A) The process is endothermic with an enthalpy change of approximately 480 kJ.

(B) The process is endothermic with an enthalpy change of approximately 240 kJ.

(C) The process is exothermic with an enthalpy change of approximately 480 kJ.

(D) The process is exothermic with an enthalpy change of approximately 240 kJ.

(E) The process is exothermic with an enthalpy change of approximately 1,800 kJ.

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261. The enthalpy of combustion of ethanol (C2H5OH(l)) is shown above. Using this information and the data in the table above, the standard heat of formation of CO2(g) is closest to:

(A) –1,080 kJ mol−1

(B) –540 kJ mol−1

(C) –510 kJ mol−1

(D) –390 kJ mol−1

(E) –250 kJ mol−1

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262. What is the standard enthalpy change, image, of the reaction represented above?

(A) –24.3 kJ

(B) –58.3 kJ

(C) 24.3 kJ

(D) 58.3 kJ

(E) 77.7 kJ

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263. When CO3(s) is added to a beaker of dilute HCl(aq) at 298 K, the beaker gets cold and a gas is produced. Which of the following indicates the correct signs for ΔG, ΔH, and ΔS for the reaction represented above?

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264. Considering the data in the table above, which of the following must be true of the reaction?

(A) A catalyst is present.

(B) The reaction order is zero.

(C) The reaction is at equilibrium.

(D) The enthalpy change of the reaction is zero.

(E) This reaction is occurring at a temperature above 298 K.

Questions 265–269 refer to the data in the following table.

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265. What is the value of ΔH°298 for reaction Z?

(A) 90 kJ mol−1

(B) –90 kJ mol−1

(C) 172 kJ mol−1

(D) –172 kJ mol−1

(E) 213 kJ mol−1

266. Reactions for which the value of Kp will increase under greater pressure include which of the following?

(A) X only

(B) Z only

(C) X and Z

(D) The values of Kp decrease with increased pressure

(E) None of the Kp values will increase

267. Reactions for which the value Kp will increase if the temperature is raised above 298 K include which of the following?

(A) X only

(B) Y only

(C) Z only

(D) X and Y only

(E) Y and Z only

268. Which of the following most accurately describes the ΔS of reaction Z?

(A) Positive, because there are more products than reactants.

(B) Positive, because there are more states of matter in the products.

(C) Positive, because there is only one species of reactant but there are two species of product.

(D) Negative, because two moles of gas are converted to a solid and one mole of gas.

(E) Negative, because a pure element was formed.

269. Which of the following statements most accurately describes the rates of reactions X and Y?

(A) X will occur more rapidly than Y because the ΔH is more positive.

(B) Y will occur more rapidly than X because the ΔH is less positive.

(C) X will occur more rapidly than Y because the ΔS and ΔG are more positive.

(D) Y will occur more rapidly than X because the ΔS and ΔG are less positive.

(E) Thermodynamic data for overall reactions do not indicate anything about the rate of a chemical reaction.