AP Chem: Unit 6 Test Review

2CO(g)+C(g)→C3O2(g)ΔH°=127.3kJ/molrxn The equation shown above represents an endothermic reaction between CO(g) and C(g). What is the amount of heat absorbed when 1.00mol of CO(g) reacts with an excess C(g) ? A 31.8kJ31.8kJ B 63.7kJ63.7kJ C 127.3kJ127.3kJ D 254.6kJ

b

3 C2H2(g) → C6H6(g) What is the standard enthalphy change ΔHo, for the reaction represented above? (ΔHof of C2H2(g) is 230 kJ mol-1; (ΔHof of C6H6(g) is 83 kJ mol-1;) A -607 kJ B -147 kJ C -19 kJ D +19 kJ E +773 kJ

A

2Al(s)+Fe2O3(s)→2Fe(s)+Al2O3(s)ΔH°=−850kJ/molrxn The chemical equation shown above represents the thermite reaction. What is the approximate amount of heat released when 108g of Al(s) reacts with excess Fe2O3(s) ? A 210kJ210kJ B 430kJ430kJ C 850kJ850kJ D 1700kJ

D

6. SampleInitial Volume (mL)Initial Temperature (C∘)1125.036.02250.018.0 The table provides data for two CH3OH(l) samples. Based on this information, which of the following statements describes what happens when these samples are initially mixed, and why? A Thermal energy is transferred between the CH3OHCH3OH molecules in sample 1 and the CH3OHCH3OH molecules in sample 2 because both samples contain the same substance. B The CH3OHCH3OH molecules from sample 2 transfer thermal energy to the CH3OHCH3OH molecules from sample 1 through collisions because there are more moles of molecules in sample 2. C The CH3OHCH3OH molecules from sample 1 transfer thermal energy to the CH3OHCH3OH molecules from sample 2 through collisions because sample 1 has a higher density. D The CH3OHCH3OH molecules from sample 1 transfer thermal energy to the CH3OHCH3OH molecules from sample 2 through collisions because the average kinetic energy of the molecules in sample 1 is greater.

D

9. SubstanceMass (g)Initial Temperature (°C)ΔT (°C)Specific Heat Capacity(J/g⋅°C)qAl20.090.−5.90.90?H2O40.02564.2? For an experiment, a 20.0 g piece of Al was placed inside an insulated cup filled with 40.0 g of H2O. The data are given in the table above. Assuming no heat is absorbed by the container or the surroundings, which of the following equations provides the correct mathematical relationship for the transfer of heat q between Al and H2O? A −qAl=12×qH2O−qAl=12×qH2O B −qAl=6×qH2O−qAl=6×qH2O C −qAl=2×qH2O−qAl=2×qH2O D −qAl=qH2O−qAl=qH2O

D

The cooling curve above shows how the temperature of a sample varies with time as the sample goes through phase changes. The sample starts as a gas, and heat is removed at a constant rate. At which time does the sample contain the most liquid? A t1 B t2 C t3 D t4 E t5 Related Content & Skills Topic6.5 SkillSkill 5.D

D

11. The table above provides the values for some physical properties of H2S and H2O. Approximately, how many moles of H2S must be condensed to release as much heat as would be released when 1 mole of H2O is condensed? A 0.5 mole of H2SH2S B 1 mole of H2SH2S C 2 moles of H2SH2S D 4 moles of H2SH2S

C

A cube of ice is added to some hot water in a rigid, insulated container, which is then sealed. There is no heat exchange with the surroundings. What has happened to the total energy and the total entropy when the system reaches equilibrium? A EnergyEntropyRemains constantRemains constant B EnergyEntropyRemains constantDecreases C EnergyEntropyRemains constantIncreases D EnergyEntropyDecreasesIncreases E EnergyEntropyIncreasesDecreases Related Content & Skills Topic9.1 SkillSkill 4.A

C

C2H6(g)+72O2(g)→2CO2(g)+3H2O(l)ΔH°=−1560kJC(graphite)+O2(g)→CO2(g)ΔH°=−394kJ Given the equations and the values of ΔH° for the combustion of C2H6(g) and the combustion of C(graphite) represented above, which of the following additional information is needed to determine the values of ΔH° for the overall reaction 2C(graphite)+3H2(g)→C2H6(g) ? A C(diamond)→C(graphite) ΔH°=−2kJ C(diamond)→C(graphite) ΔH°=−2kJ B C2H4(g)+H2(g)→C2H6(g) ΔH°=−134kJC2H4(g)+H2(g)→C2H6(g) ΔH°=−134kJ C H2(g)+12O2(g)→H2O(l) ΔH°=−286kJH2(g)+12O2(g)→H2O(l)⁢ ΔH°=−286kJ D H2O(l)→H2O(g) ΔH°=+41kJH2O(l)→H2O(g) ΔH°=+41kJ

C

HCl(aq)+NH3(aq)→NH4+(aq)+Cl−(aq) The chemical reaction between HCl(aq) and NH3(aq) is represented above. A student combines equimolar amounts of HCl(aq) and NH3(aq), both solutions initially at 24°C, in a coffee-cup calorimeter. The student observes that the mixture reaches a temperature of 28°C. Based on the experimental results, which of the following can be concluded about the reaction? A It is an endothermic process, because energy is released by the reaction and is gained by the reaction mixture. B It is an endothermic process, because energy is absorbed by the reaction and is lost from the reaction mixture. C It is an exothermic process, because energy is released by the reaction and is gained by the reaction mixture. D It is an exothermic process, because energy is absorbed by the reaction and is lost from the reaction mixture.

C

K(s)+ ½ Cl2(g) → KCl(s) ΔH° = -437kJ/molrxn The elements K and Cl react directly to form the compound KCl according to the equation above. Refer to the information above and the table below to answer the questions that follow. Cl2(g) + 2e- → 2Cl-(g) Which of the following expressions is equivalent to ΔHo for the reaction represented above? A x + y B x - y C x + 2y D x2−yMathType@MTEF@5@5@+=feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaSaaaeaacaWG4baabaGaaGOmaaaacqGHsislcaWG5baaaa@39AA@ Related Content & Skills Topic6.9 SkillSkill 5.F

C

K(s)+ ½ Cl2(g) → KCl(s) ΔH° = -437kJ/molrxn The elements K and Cl react directly to form the compound KCl according to the equation above. Refer to the information above and the table below to answer the questions that follow. How much heat is released or absorbed when 0.050 mol of Cl2(g) is formed from KCl(s)? A 87.4 kJ is released B 43.7 kJ is released C 43.7 kJ is absorbed D 87.4 kJ is absorbed Related Content & Skills Topic6.6 SkillSkill 5.F

C

Na2S2O3(aq)+4NaOCl(aq)+2NaOH(aq)→2Na2SO4(aq)+4NaCl(aq)+H2O(l) The enthalpy change for the reaction represented by the chemical equation shown above is ΔH°=−1236kJ/molrxn. When 2.00mol of NaOCl(aq) reacts completely with an excess of Na2S2O3(aq) and of NaOH(aq), which of the following enthalpy changes occurs? A 618kJ618kJ of heat is absorbed. B 2470kJ2470kJ of heat is absorbed. C 618kJ618kJ of heat is released. D 2470kJ2470kJ of heat is released.

C

Particulate models of the evaporation of liquid water and the condensation of water vapor are shown above. Based on these models, which of the following accurately compares the energy changes associated with each of the phase changes? A The amount of energy absorbed by one mole of water molecules as they escape the liquid is greater than the amount of energy released by one mole of water molecules as they come together to form a liquid. B The amount of energy absorbed by one mole of water molecules as they escape the liquid is less than the amount of energy released by one mole of water molecules as they come together to form a liquid. C The amount of energy absorbed by one mole of water molecules as they escape the liquid is equal to the amount of energy released by one mole of water molecules as they come together to form a liquid. D The amount of energy absorbed by one mole of water molecules escaping the liquid can be either greater than or less than the amount of energy released by one mole of water molecules as they come together.

C

Reaction 1:2O3(g)→3O2(g)Reaction 2:?Overall reaction:2O3(g)+2NO(g)→2NO2(g)+2O2(g) The enthalpy of the overall reaction represented above can be determined by adding the enthalpies of reactions 1 and 2. Which of the following could be reaction 2 ? A NO(g)+O(g)→NO2(g) NO(g)+O(g)→NO2(g) B (NO)2(g)→2NO(g)(NO)2(g)→2NO(g) C 2NO(g)+O2(g)→2NO2(g)2NO(g)+O2(g)→2NO2(g) D 2NO2(g)+O3(g)→N2O5(g)+O2(g)

C

Refer to the following. PCl5(g) ⇄ PCl3(g)+Cl2(g) PCl5(g) decomposes into PCl3(g) and Cl2(g) according to the equation above. A pure sample of PCl5(g) is placed in a rigid, evacuated 1.00L container. The initial pressure of the PCl5(g) is 1.00 atm. The temperature is held constant until the PCl5(g) reaches equilibrium with its decomposition products. The figures below show the initial and equilibrium conditions of the system. As the reaction progresses toward equilibrium, the rate of the forward reaction A increases until it becomes the same as the reverse reaction rate at equilibrium B stays constant before and after equilibrium is reached C decreases to become a constant nonzero rate at equilibrium D decreases to become zero at equilibrium Related Content & Skills Topic7.1 SkillSkill 4.A

C

SubstanceΔH∘f(kJ/mol)CH4(g)−75O2(g)0CO2(g)−390H2O(g)−240 Natural gas consists primarily of CH4, which is combusted according to the following chemical equation. CH4(g)+2O2(g)→CO2(g)+2H2O(g) Based on the standard enthalpies of formation in the table above, which of the following expressions give the approximate enthalpy change for the reaction (ΔH°rxn) ? A ΔH°rxn=(−75kJ/mol)−[(−390kJ/mol)+2(−240kJ/mol)]ΔHrxn°=(−75kJ/mol)−[(−390kJ/mol)+2(−240kJ/mol)] B ΔH°rxn=(−75kJ/mol)−[(−390kJ/mol)+(−240kJ/mol)]ΔHrxn°=(−75kJ/mol)−[(−390kJ/mol)+(−240kJ/mol)] C ΔH°rxn=[(−390kJ/mol)+2(−240kJ/mol)]−(−75kJ/mol)ΔHrxn°=[(−390kJ/mol)+2(−240kJ/mol)]−(−75kJ/mol) D ΔH°rxn=[(−390kJ/mol)+(−240kJ/mol)]−(−75kJ/mol

C

Type of BondAverage Bond Enthalpy (kJ/mol)O−O150O=O500 2O3(g)→3O2(g) ΔH∘rxn=−300kJ/molrxn The conversion of ozone to diatomic oxygen is represented by the equation above. Based on the data in the table above, what is the approximate average bond enthalpy for the oxygen-to-oxygen bonds in ozone? A 0kJ/mol0kJ/mol B 150kJ/mol150kJ/mol C 300kJ/mol300kJ/mol D 500kJ/mol

C

When pellets of NaOH(s) are added to a flask of water, it is observed that the temperature of the water increases as the pellets dissolve. Which of the following claims about the observed dissolution of NaOH(s) in water is most accurate? A It is an endothermic process because heat energy is absorbed by the water as the NaOH(s)NaOH(s) dissolves in it. B It is an endothermic process because heat energy is released by the water as the NaOH(s)NaOH(s) dissolves in it. C It is an exothermic process because heat energy is absorbed by the water as the NaOH(s)NaOH(s) dissolves in it. D It is an exothermic process because heat energy is released by the water as the NaOH(s)NaOH(s) dissolves in it.

C

An advertisement for a commercial hand warmer claims that the hand warmer works because a chemical reaction in the hand warmer draws out the body's own natural heat, causing a warming effect. Which of the following states the accuracy of the claim in the advertisement and best provides a correct scientific justification of the claim? A The advertisement's claim is inaccurate because heat flowing from the hands to the warmer would only happen if the chemical reaction was endothermic, which would cause the hands to feel colder. B The advertisement's claim is inaccurate because heat flowing from the hands to the warmer would only happen if the chemical reaction was exothermic, which would cause the hands to feel colder. C The advertisement's claim is accurate because heat flowing from the hands to the warmer would only happen if the chemical reaction was endothermic, which would cause the hands to feel warmer. D The advertisement's claim is accurate because heat flowing from the hands to the warmer would only happen if the chemical reaction was exothermic, which would cause the hands to feel warmer.

A

Bond TypeAverage Bond Enthalpy (kJ/mol)C−H414C−O360C=O799O−H464 The combustion of methane proceeds according to the chemical equation CH4+2 O2→CO2+2 H2O. The table above provides the average bond enthalpy for selected bonds. The calculated enthalpy change for the reaction, ΔHrxn, is −802 kJ/mol. Which of the following provides the mathematical procedure to estimate the bond enthalpy per mole of O2? A 12[−802 +2(799)+4(464)−4(414)]kJ/mol12[−802 ⁢+2(799)+4(464)−4(414)]kJ/mol B 2[−802+799+2(464)−2(414)]kJ/mol2[−802+799+2(464)−2(414)]kJ/mol C 12[−802−2(360)+4(464)+4(414)]kJ/mol12[−802−2(360)+4(464)+4(414)]kJ/mol D 2[−802−360+2(464)+414]kJ/mol2[−802−360+2(464)+414]kJ/mol

A

SubstanceΔH∘f(kJ/mol)CaCO3(s)−1210CaO(s)−640CO2(g)−390 CaCO3 decomposes according to the balanced equation CaCO3(s)→CaO(s)+CO2(g). Based on the standard enthalpies of formation provided in the table above, what is the approximate enthalpy change of the reaction? A −180kJ−180kJ B +180kJ+180kJ C −1460kJ−1460kJ D +1460kJ+1460kJ

A

The following questions relate to the graph below. The graph shows the temperature of a pure substance as it is heated at a constant rate in an open vessel at 1.0 atm pressure. The substance changes from the solid to the liquid to the gas phase. Which of the following best describes what happens to the substance between t4 and t5? A The molecules are leaving the liquid phase. B The solid and liquid phases coexist in equilibrium. C The vapor pressure of the substance is decreasing. D The average intermolecular distance is decreasing. E The temperature of the substance is increasing. Related Content & Skills Topic6.5 SkillSkill 4.C

A

7. The graph above shows the changes in temperature recorded for the 2.00 L of H2O surrounding a constant-volume container in which a 1.00 g sample of benzoic acid was combusted. Assume that heat was not absorbed by the container or lost to the surroundings, that the density of H2O is 1.00g/mL, and that the specific heat capacity of H2O is about 4.2J/g⋅°C. Based on this information, estimate how much heat was released from the combustion of the benzoic acid sample. A 0.013kJ0.013kJ B 25kJ25kJ C 180kJ180kJ D 210kJ210kJ

B

12. The heating curve for 1.0 mole of Na, initially at 25.0°C, is shown above at the left. Which of the following best explains the change in heat when 0.50 mole of Na undergoes the transition shown in the diagram above to the right? A Approximately 13kJ13kJ of heat are absorbed as a result of the increase in potential energy between the NaNa atoms. B Approximately 49kJ49kJ of heat are absorbed to overcome the attractive forces acting between NaNa atoms. C Approximately 98kJ98kJ of heat are released as a result of the decrease in the kinetic energy of the NaNa atoms. D Approximately 120kJ120kJ of heat are released to decrease the potential energy between NaNa atoms.

B

A 100g sample of a metal was heated to 100oC and then quickly transferred to an insulated container holding 100g of water at 22oC. The temperature of the water rose to reach a final temperature of 35oC. Which of the following can be concluded? A The metal temperature changed more than the water temperature did; therefore the metal lost more thermal energy than the water gained. B The metal temperature changed more than the water temperature did, but the metal lost the same amount of thermal energy as the water gained. C The metal temperature changed more than the water temperature did; therefore the heat capacity of the metal must be greater than the heat capacity of the water. D The final temperature is less than the average starting temperature of the metal and the water; therefore the total energy of the metal and water decreased. Related Content & Skills Topic6.3 SkillSkill 4.A

B

A student carefully drops a 9.0g solid Zn pellet initially at 50.0°C into an insulated cup containing 30.0g of water at 27.8°C. The student predicts that the temperature of the water will increase after the pellet is added. Which of the following statements is the best justification for the student's prediction? A The metallic bonds between ZnZn atoms will break when the ZnZn is exposed to the water molecules, releasing energy that will be absorbed by the water molecules. B Collisions between the water molecules and the surface of the ZnZn pellet will result in the transfer of energy, increasing the average kinetic energy of the water molecules. C The strength of the hydrogen bonds between the water molecules will increase when the ZnZn pellet is added, decreasing the average kinetic energy of the water molecules. D Collisions between ZnZn atoms in the solid will increase in frequency when the ZnZn is exposed to the water molecules, resulting in the transfer of energy to the surroundings.

B

Bond TypeAverage Bond EnthalpyH−H436kJ/molCl−Cl243kJ/molH−Cl432kJ/mol The formation of hydrogen chloride gas is represented by the chemical equation H2(g)+Cl2(g)→2HCl(g). Based on the bond enthalpy data in the table above, what is the approximate enthalpy change for the reaction? A −247kJ/molrxn−247kJ/molrxn B −185kJ/molrxn−185kJ/molrxn C +185kJ/molrxn+185kJ/molrxn D +247kJ/molrxn+247kJ/molrxn

B

Chemical EquationΔH°(kJ/molrxn)H2(g)+12O2(g)→H2O(l)−286N2(g)+3O2(g)+H2(g)→2HNO3(l)−348 The table above provides the values for the standard enthalpy change for two chemical reactions. A student needs to calculate the enthalpy change for the reaction 2HNO3(l)→N2O5(g)+H2O(l) under standard conditions using Hess's law. In addition to the values given in the table, what other information will the student need to perform the calculation? A ΔH∘fΔHf∘ for N2(l)N2(l) B ΔH∘fΔHf∘ for N2O5(g)N2O5(g) C ΔH∘fΔHf∘ for H2O(g)H2O(g) D ΔH∘fΔHf∘ for H2(l)

B

K(s)+ ½ Cl2(g) → KCl(s) ΔH° = -437kJ/molrxn The elements K and Cl react directly to form the compound KCl according to the equation above. Refer to the information above and the table below to answer the questions that follow. Which of the values of ∆Ho for a process in the table is (are) less than zero (i.e., indicate(s) an exothermic process)? A z only B y and z only C x, y, and z only D w, x, y, and z Related Content & Skills Topic6.16.6 SkillSkill 6.C

B

SubstanceΔH°f(kJ/mol)SO2(g)−296.1SO3(g)−395.2O2(g)0.0 Based on the information above, what is ΔH° for the reaction SO2(g)+12O2(g)→SO3(g) ? A −591.3kJ/molrxn−591.3kJ/molrxn B −99.1kJ/molrxn−99.1kJ/molrxn C +99.1kJ/molrxn+99.1kJ/molrxn D +591.3kJ/molrxn

B

The following questions relate to the graph below. The graph shows the temperature of a pure substance as it is heated at a constant rate in an open vessel at 1.0 atm pressure. The substance changes from the solid to the liquid to the gas phase. The substance is at its normal freezing point at time A t1 B t2 C t3 D t4 E t5 Related Content & Skills Topic6.5 SkillSkill 5.D

B

Two aqueous NaCl solutions of equal volume and concentration were kept in flasks and held at different temperatures. The two solutions were combined in a larger flask. Based on this information, which of the following predictions is correct? A The average kinetic energy of the particles in the cooler solution will decrease as they collide with the particles from the warmer solution. B The average kinetic energy of the particles in the cooler solution will increase as they collide with the particles from the warmer solution. C The particles from the cooler solution and the particles from the warmer solution will reach thermal equilibrium through collisions, at which time the average kinetic energy of the particles in the mixture will be lower than the average kinetic energy that the particles had in the cooler solution. D The particles from the cooler solution and the particles from the warmer solution will reach thermal equilibrium through collisions, at which time the average kinetic energy of the particles in the mixture will be higher than the average kinetic energy that the particles had in the warmer solution.

B