AP Chemistry Topic 3.5 & 3.6

A gaseous air fuel mixture in a sealed car engine cylinder has an initial volume of 600.mL at 1.0atm. To prepare for ignition of the fuel, a piston moves within the cylinder, reducing the volume of the air fuel mixture to 50.mL at constant temperature. Assuming ideal behavior, what is the new pressure of the air fuel mixture?

• About 0.083atm, because the initial volume of the gas mixture was 12 times larger than its final volume.

• About 12atm, because the volume of the gas mixture decreased by a factor of 12.

• About 120.atm, because the initial volume of the gas mixture was 120 times larger than its final volume.

• About 550.atm, because the change in the volume of the gas mixture was 550.mL

At 10.°C, 20.g of oxygen gas exerts a pressure of 2.1atm in a rigid, 7.0L cylinder. Assuming ideal behavior, if the temperature of the gas was raised to 40.°C, which statement indicates the new pressure and explains why?

• 1.9atm, because the pressure P decreases by the proportion 283/313.

• 2.3atm, because the pressure P increases by the proportion 313/283.

• 0.52atm, because the pressure P decreases by the proportion 10/40

• 8.4atm, because the pressure P increases by the proportion 40/10..

Two sealed, rigid 5.0L containers each contain a gas at the same temperature but at a different pressure, as shown above. Also shown are the results of transferring the entire contents of container 1 to container 2. No gases escape during the transfer. Assuming ideal behavior, which statement is correct regarding the total pressure of the gases after they are combined?

• The total pressure of the gases in the mixture is the sum of the initial pressures of oxygen gas and nitrogen gas because pressure only depends on the total amount of gas when volume and temperature are held constant.

• The total pressure of the gases in the mixture is lower than the sum of the initial pressures of oxygen and nitrogen because some of the energy of the particles will be lost due to an increase in the number of collisions.

• The total pressure of the gases in the mixture is higher than the sum of the initial pressures of oxygen and nitrogen because of the intermolecular forces that develop between oxygen and nitrogen molecules.

• The total pressure of the gases in the mixture cannot be determined because the actual value of the temperature is not given.

The diagrams above use arrows to represent the speed of a gas particle. Which of the diagrams best represents the speed of the particles of a gas at a fixed temperature, and why?

• Diagram 1, because all the particles have the same speed.

• Diagram 1, because the particles are moving in different directions.

• Diagram 2, because the particles have a net kinetic energy of zero.

• Diagram 2, because the particles have a variety of different speeds.

Tags

NGSS.HS-PS3-2

The two gas samples represented in the graph above are at the same temperature. Which of the following statements about the gases is correct?

• The molecules of gas Z have a higher average kinetic energy than the molecules of gas X.

• There are fewer molecules in the sample of gas Z than in the sample of gas X.

• Gas Z has a smaller molar mass than gas X.

• Gas Z has a greater molar mass than gas X.

Tags

NGSS.HS-PS3-2

The diagram above shows the distribution of speeds for a sample of O2(g). Which of the following graphs shows the distribution of speeds for the same sample at a higher temperature (dashed line) ?

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Tags

NGSS.HS-PS1-5

NGSS.HS-PS3-4

Equimolar samples of CH₄(g) and C₂H₆(g) are in identical containers at the same temperature. The C₂H₆(g) deviates much more from ideal behavior than the CH₄(g) does. Which of the following best helps explain this deviation?

• C₂H₆ molecules have a larger, more polarizable electron cloud than CH₄ molecules do.

• C₂H₆ molecules have more hydrogen bonding than CH₄ molecules do.

• The C₂H₆ molecules have a greater average kinetic energy than the CH₄ molecules have.

• The C₂H₆ molecules have a greater average speed than the CH₄ molecules have.

The gases CO₂(g) and NH₃(g) can be liquefied at 20^oC by compressing them to sufficiently high pressures. A student claims that NH₃ (g) can be liquefied at a lower pressure than CO₂ (g) can be liquefied. Which of the following is the best justification for this claim?

• At 20^oC, the average speed of NH₃ molecules is greater than that CO₂ molecules because NH₃ molecules have less mass than CO₂ molecules have.

• CO₂ is a nonpolar molecule that has no significant intermolecular forces, whereas NH₃ has strong London dispersion intermolecular forces.

• Both CO₂ and NH₃ are nonpolar molecules that have only London dispersion intermolecular forces, but the larger electron cloud of CO₂ molecules causes it to have stronger intermolecular forces.

• CO₂ is a nonpolar molecule that has London dispersion intermolecular forces that are weaker than the dipole-dipole and London dispersion forces between the polar NH₃ molecules.

The graph above shows how a particular real gas deviates from ideal behavior at very high pressures. Based on this information, which of the following is most likely the gas and gives the reason based on kinetic molecular theory?

• H₂, because it has the smallest mass.

• N₂, because its molecules have a triple bond.

• Ne, because it has a completely filled valence shell.

• SO₂, because it has the largest molecular volume.

Tags

NGSS.HS-PS1-3

How many grams of N₂O₅ gas  are in a sample that has a volume of 2.00 Liters at 298 K and 100. kPa of pressure.  

• 8.72 grams
• 0.0807 grams
• 12.3 grams
• 883 grams