Question

use the references to access important values if needed for this question.
a 1.33 mol sample of kr gas is confined in a 31.2 liter container at 12.9 °c.
if the temperature of the gas sample is decreased to -10.9 °c, holding the volume constant, the pressure will decrease because:
choose all that apply.
□ with higher average speeds, the molecules hit the walls of the container more often.
□ as the average speed increases, the number of molecule-wall collisions decreases.
□ at lower temperatures molecules have lower average speeds.
□ with lower average speeds, on average the molecules hit the walls of the container with less force.
□ none of the above
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Explanation:

According to the kinetic - molecular theory of gases:

• When the temperature decreases (from \(12.9^{\circ}C\) to \(- 10.9^{\circ}C\)), the average speed of gas molecules (\(v_{rms}=\sqrt{\frac{3RT}{M}}\), where \(R\) is the gas constant, \(T\) is the temperature in Kelvin, and \(M\) is the molar mass) decreases.
• At lower temperatures, molecules have lower average speeds. Since the force exerted by gas molecules on the container walls is related to their speed (momentum change per collision, \(F=\Delta p/\Delta t\), and \(\Delta p = mv - (- mv)=2mv\) for an elastic collision with the wall, where \(m\) is the mass of the molecule and \(v\) is the speed perpendicular to the wall), with lower average speeds, on average the molecules hit the walls of the container with less force.
• As the average speed of molecules decreases (because \(T\) decreases), the number of molecule - wall collisions also decreases (fewer collisions per unit time since molecules are moving more slowly).

Answer:

• With lower average speeds, on average the molecules hit the walls of the container with less force.
• At lower temperatures molecules have lower average speeds.
• As the average speed increases, the number of molecule - wall collisions decreases.