AP Chemistry — Unit 6 Progress Check: MCQ

1.

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. It is an exothermic process, because energy is released by the reaction and is gained by the reaction mixture.

2.

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) dissolves in it.

B)

It is an endothermic process because heat energy is released by the water as the NaOH(s) dissolves in it.

C)

It is an exothermic process because heat energy is absorbed by the water as the NaOH(s) dissolves in it.

D)

It is an exothermic process because heat energy is released by the water as the NaOH(s) dissolves in i

C. It is an exothermic process because heat energy is absorbed by the water as the NaOH(s) dissolves in it.

3.

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. 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.

4.

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 Zn atoms will break when the Zn 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 Zn 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 Zn pellet is added, decreasing the average kinetic energy of the water molecules.

D)

Collisions between Zn atoms in the solid will increase in frequency when the Zn is exposed to the water molecules, resulting in the transfer of energy to the surroundings.

B. Collisions between the water molecules and the surface of the Zn pellet will result in the transfer of energy, increasing the average kinetic energy of the water molecules.

5.

Two aqueous 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. The average kinetic energy of the particles in the cooler solution will increase as they collide with the particles from the warmer solution.

6.

Initial Volume (mL)

1. 125.0

2. 250.0

Initial Temperature (*C)

1. 36.0

2. 18.0

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 CH₃OH molecules in sample 1 and the CH₃OH molecules in sample 2 because both samples contain the same substance.

B)

The CH₃OH molecules from sample 2 transfer thermal energy to the CH₃OH molecules from sample 1 through collisions because there are more moles of molecules in sample 2.

C)

The CH₃OH molecules from sample 1 transfer thermal energy to the CH₃OH molecules from sample 2 through collisions because sample 1 has a higher density.

D)

The CH₃OH molecules from sample 1 transfer thermal energy to the CH₃OH molecules from sample 2 through collisions because the average kinetic energy of the molecules in sample 1 is greater.

D. The CH₃OH molecules from sample 1 transfer thermal energy to the CH₃OH molecules from sample 2 through collisions because the average kinetic energy of the molecules in sample 1 is greater.

7.

(Graph on AP Classroom)

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) 0.013kJ

B) 25 kJ

C) 180 kJ

D) 210 kJ

B. 25 kJ

8.

(Table on AP Classroom)

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 = 10 * qH₂O

B) -qAl = 5 * qH₂O

C) -qAl = 2 * qH₂O

D) -qAl = qH₂O

D. -qAl = qH₂O

9.

(Picture on AP Classroom)

A student dissolves 8.00 g of NH₄NO₃(s) in 100. g of H₂O(l) in a coffee-cup calorimeter. Based on the initial and final temperatures of the mixture in degrees Celsius shown in the diagram above the laboratory setup, what is the calculated ∆T of the water reported to the appropriate number of significant figures?

A) -5.500°C

B) -5.50°C

C) -5.5°C

D) -6°C

C. -5.5°C

10.

(Picture on AP Classroom)

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 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.

11.

(Table on AP Classroom)

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 H₂S

B) 1 mole of H₂S

C) 2 moles of H₂S

D) 4 moles of H₂S

C. 2 moles of H₂S

12.

(Table and Picture on AP Classroom)

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 trans

A)

Approximately 13kJ of heat are absorbed as a result of the increase in potential energy between the Na atoms.

B)

Approximately 49kJ of heat are absorbed to overcome the attractive forces acting between Na atoms.

C)

Approximately 98kJ of heat are released as a result of the decrease in the kinetic energy of the Na atoms.

D)

Approximately 120kJ of heat are released to decrease the potential energy between Na atoms.

B. Approximately 49 kJ of heat are absorbed to overcome the attractive forces acting between Na atoms.

13.

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 ∆H° = -1236 kJ/molrxn. When 2.00 mol of NaCl(aq) reacts completely with an excess of Na₂S₂O₃(aq) and NaOH(aq), which of the following enthalpy changes occurs

A)

618kJ of heat is absorbed.

B)

2470kJ of heat is absorbed.

C)

618kJ of heat is released.

D)

2470kJ of heat is released.

C. 618 kJ of heat is released.

14.

2Al(s) + Fe₂O₃(s) → 2Fe(s) + Al₂O₃(s)

∆H° = -850 kJ/molrxn

The chemical equation shown above represents the thermite reaction. What is the approximate amount of heat released when 108 g of Al(s) reacts with excess Fe₂O₃(s)?

A) 210 kJ

B) 430 kJ

C) 850 kJ

D) 1700 kJ

D. 1700 kJ

15.

2CO(g) + C(g) → C₃O₂(g)

∆H° = 127.3 kJ/molrxn

The equation shown above represents an endothermic reaction between CO(g) and C(g). What is the amount of heat absorbed when 1.00 mol of CO(g) reacts with an excess C(g).

A) 31.8kJ

B) 63.7kJ

C) 127.3kJ

D) 254.6 kJ

B. 63.7 kJ

16.

(Table on AP Classroom)

2O₃(g) → 3O₂(g)

∆H° = -300 kJ/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) 0 kJ/mol

B) 150 kJ/mol

C) 300 kJ/mol

D) 500 kJ/mol

C. 300 kJ/mol

17.

The combustion of methane proceeds according to the chemical equation CH₄ + 2O₂ → CO₂ + 2H₂O. The table above provides the average bond enthalpy for selected bonds. The calculated enthalpy change for the reaction, ∆Hrxn, is -802 kJ/mol. Which of the following provides the mathematical procedure to estimate the bond enthalpy per mole of O₂?

A)

½[−802 + 2(799) + 4(464) − 4(414)] kJ/mol

B)

2[−802 + 799 + 2(464) − 2(414) ]kJ/mol

C)

½[−802 − 2(360) + 4(464) + 4(414)] kJ/mol

D)

2[-802 - 360 + 2(464) + 414] kJ/mol

A. ½[-802 + 2(799) + 4(464) - 4(414)] kJ/mol

18.

(Table on AP Classroom)

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

B)

−185kJ/molrxn

C)

+185kJ/molrxn

D)

+247kJ/molrxn

B. -185 kJ/molrxn

19.

(Table on AP Classroom)

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) -180 kJ

B) +180 kJ

C) -1460 kJ

D) +1460 kJ

B. +180 kJ

20.

Based on the information above, what is ∆H° for the reaction SO₂(g) + ½O₂(g) → SO₃(g)?

A)

−591.3kJ/molrxn

B)

−99.1kJ/molrxn

C)

+99.1kJ/molrxn

D)

+591.3kJ/molrxn

B. -99.1 kJ/molrxn

21.

(Table on AP Classroom)

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 (∆H°rxn)?

A)

ΔHrxn° = (−75kJ/mol) − [(−390kJ/mol) + 2(−240kJ/mol)]

B)

ΔHrxn° = (−75kJ/mol) − [(−390kJ/mol) + (−240kJ/mol)]

C)

ΔHrxn° = [(−390kJ/mol) + 2(−240kJ/mol)] − (−75kJ/mol)

D)

ΔHrxn° = [(−390kJ/mol) +(−240kJ/mol)] − (−75kJ/mol)

C. ∆H°rxn = [(-390 kJ/mol) + 2(-240 kJ/mol)] - (-75 kJ/mol)

22.

C₂H₆(g) + ⁷⁄₂O₂(g) → 2CO₂(g) + 3H₂O(l)

∆H° = -1560 kJ

C(graphite) + O₂(g) → CO₂(g)

∆H° = -394 kJ

Given the equations and the values of ∆H° 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 ∆H° for the overall reaction 2C(graphite) + 3H₂(g) → C₂H₆(g)?

A)

C(diamond)→C(graphite) ΔH°=−2kJ

B)

C₂H₄(g)+H₂(g)→C₂H₆(g) ΔH°=−134kJ

C)

H₂(g)+½O₂(g)→H₂O(l)⁢ ΔH°=−286kJ

D)

H₂O(g)→H₂O(g) ΔH°=+41kJ

C. H₂(g) + ½O₂(g) → H₂O(l)

∆H° = -286 kJ

23.

Reaction 1: 2O₃(g) → 3O₂(g)

Reaction 2: ?

Overall Reaction: 2O₃(g) + 2NO(g) → 2NO(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)

B)

(NO)₂(g)→2NO(g)

C)

2NO(g)+O₂(g)→2NO₂(g)

D)

2NO₂(g)+O₃(g)→N₂O₅(g)+O₂(g)

C. 2NO(g) + O₂(g) → 2NO₂(g)

24.

(Table on AP Classroom)

The table above provides the values for the standard enthalpy change for two chemical reactions. A student need 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 information will the student need to perform the calculation?

A)

ΔHf∘ for N₂(l)

B)

ΔHf∘ for N₂O₅(g)

C)

ΔHf∘ for H₂O(g)

D)

ΔHf∘ for H₂(l)

B. ∆H°f for N₂O₅(g)