AP®ChemistryCollege BoardExam QuestionsUnit 3: Intermolecular Forces & PropertiesGas Laws

Gas Laws (College Board AP® Chemistry)

Exam Questions

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Gas Laws

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Gas Laws

1a3 marks

CS2(g) + 3 Cl2(g)   → CCl4(g) + S2Cl2(g)

Carbon tetrachloride , CCl4(g), can be synthesized according to the reaction represented above. A chemist runs the reaction at a constant temperature of 120°C in a rigid 25.0 L container.

Chlorine gas, Cl2(g), is initially present in the container at a pressure of 0.40 atm.

i) How many moles of Cl2(g) are in the container?

ii) How many grams of carbon disulfide, CS2(g) , are needed to react completely with the Cl2(g) ?

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1b3 marks

At 30°C the reaction is thermodynamically favorable, but no reaction is observed to However, at 120°C, the reaction occurs at an observable rate.

i) Explain how the higher temperature affects the collisions between the reactant molecules so that the reaction occurs at an observable rate at 120°

ii) The graph below shows a distribution for the collision energies of reactant molecules at 120° Draw a second curve on the graph that shows the distribution for the collision energies of reactant molecules at 30°C.

q1bii-june-2017--ap-chemistry

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1c2 marks

S2Cl2 is a product of the reaction .

i) In the box below, complete the Lewis electron-dot diagram for the S2Cl2  molecule by drawing in all of the electron pairs.

q1c-june-2017---ap-chemistry

ii) What is the approximate value of the Cl-S-S bond angle in the S2Cl2molecule that you drew in part (c)(i) ? (If the two Cl-S-S bond angles are not equal, include both angles.)

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1d2 marks

CCl4(g) can also be produced by reacting CHCl3(g) with Cl2(g) at 400°C , as represented by the equation below.

CHCl3(g) + Cl2(g)   →  CCl4(g) + HCl(g)

At the completion of the reaction a chemist successfully separates the CCl4(g) from the HCl(g) by cooling the mixture to 70°C, at which temperature the CCl4(g) condenses while the HCl(g) remains in the gaseous state.

i) Identify all types of intermolecular forces present in HCl(l) .

ii) What can be inferred about the relative strengths of the intermolecular forces in CCl4(l)  and  HCl(l) ? Justify your answer in terms of the information above.

 

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2a3 marks
q2-june-2015---ap-chemistry

Ethene, C2H4(g) (molar mass 28.1 g/mol), may be prepared by the dehydration of ethanol, C2H5OH(g) (molar mass 46.1 g/mol), using a solid catalyst. A setup for the lab synthesis is shown in the diagram above. The equation for the dehydration reaction is given below.

begin mathsize 16px style straight C subscript 2 straight H subscript 5 OH open parentheses straight g close parentheses space rightwards arrow with catalyst on top straight C subscript 2 straight H subscript 4 open parentheses straight g close parentheses space plus straight H subscript 2 straight O open parentheses straight g close parentheses space increment straight H subscript 298 superscript degree equals 45.5 space kJ divided by mol subscript r x n end subscript semicolon space increment straight S subscript 298 superscript degree equals 126 space straight J divided by open parentheses straight K. mol subscript r x n end subscript close parentheses end style

A student added a 0.200 g sample of C2H5OH(l) to a test tube using the setup shown above. The student heated the test tube gently with a Bunsen burner until all of the C2H5OH(l) evaporated and gas generation stopped. When the reaction stopped, the volume of collected gas was 0.0854 L at 0.822 atm and 305 K. (The vapor pressure of water at 305 K is 35.7 torr.)

Calculate the number of moles of C2H4(g)

i) that are actually produced in the experiment and measured in the gas collection tube and

ii) that would be produced if the dehydration reaction went to completion.

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2b1 mark

Calculate the percent yield of C2H4(g) in the experiment.

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2c2 marks

Because the dehydration reaction is not observed to occur at 298 K, the student claims that the reaction has an equilibrium constant less than 1.00 at 298 K.

Do the thermodynamic data for the reaction support the student’s claim? Justify your answer, including a calculation of ΔG°298 for the reaction. 

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2d1 mark

The Lewis electron-dot diagram for C2H4 is shown below in the box on the left. In the box on the right, complete the Lewis electron-dot diagram for C2H5OH by drawing in all of the electron pairs.

q2d-june-2015---ap-chemistry

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2e1 mark

What is the approximate value of the C–O–H bond angle in the ethanol molecule?

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2f2 marks

During the dehydration experiment, C2H4(g) and unreacted C2H5OH(g) passed through the tube into the The C2H4 was quantitatively collected as a gas, but the unreacted C2H5OH was not. Explain this observation in terms of the intermolecular forces between water and each of the two gases.

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3a2 marks
q4-june-2018---ap-chemistry

The table above gives the molecular structures and boiling points for the compounds CS2 and COS .

In terms of the types and relative strengths of all the intermolecular forces in each compound, explain why the boiling point of CS2(l) is higher than that of COS(l).

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3b2 marks

A 10.0 g sample of CS2(l) is put in an evacuated 5.0 L rigid container. The container is sealed and heated to 325 K, at which temperature all of the CS2(l) has vaporized. What is the pressure in the container once all of the CS2(l) has vaporized?

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4a1 mark

A student is doing experiments with CO2(g). Originally, a sample of the gas is in a rigid container at 299 K and 0.70 atm. The student increases the temperature of the CO2(g) in the container to 425 K.

Describe the effect of raising the temperature on the motion of the CO2(g) molecules.

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4b1 mark

Calculate the pressure of the CO2(g) in the container at 425 K.

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4c1 mark

In terms of kinetic molecular theory, briefly explain why the pressure of the CO2(g) in the container changes as it is heated to 425 K.

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4d1 mark

The student measures the actual pressure of the CO2(g) in the container at 425 K and observes that it is less than the pressure predicted by the ideal gas law. Explain this observation.

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5a1 mark
q7-june-2021---ap-chemistry

A student investigates gas behavior using a rigid cylinder with a movable piston of negligible mass, as shown in the diagram above. The cylinder contains 0.325 mol  of O2(g).

The cylinder has a volume of 7.95 L  at 25°C and 1.00 atm . Calculate the density of the O2(g), in  g/L, under these conditions.

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5b1 mark

Attempting to change the density of the O2(g), the student opens the valve on the side of the cylinder, pushes down on the piston to release some of the gas, and closes the valve again. The temperature of the gas remains constant at 25°C. Will this action change the density of the gas remaining in the cylinder? Justify your answer.

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5c1 mark

The student tries to change the density of the O2( g) by cooling the cylinder to − 55°C, which causes the volume of the gas to decrease. Using principles of kinetic molecular theory, explain why the volume of the O2( g) decreases when the temperature decreases to − 55°C.

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5d1 mark

The student further cools the cylinder to − 180°C and observes that the measured volume of the O2(g) is substantially smaller than the volume that is calculated using the ideal gas law. Assume all equipment is functioning properly. Explain why the measured volume of the O2(g) is smaller than the calculated volume. (The boiling point of O2(l) is − 183°C.)

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