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Chapter 19: Problem 14

Explain why the average velocity of air molecules in a closed auditorium is zero but their root-mean-square speed or average speed is not zero.

Short Answer

Expert verified
Answer: The average velocity of air molecules in a closed auditorium is zero because individual velocities of the molecules in various directions cancel each other out, resulting in no net displacement. However, their root-mean-square speed and average speed are not zero because these are scalar quantities and are not affected by the direction of motion. These quantities provide information about the magnitude of motion experienced by the molecules, which remains non-zero due to their constant random motion.

Step by step solution

01

Understanding Average Velocity

Average velocity is a vector quantity that is calculated by taking the total displacement (change in position) of an object and dividing it by the total time taken to cover that displacement. If the object returns to its starting position, its average velocity is zero since there is no net displacement.
02

Understanding Root-Mean-Square Speed

Root-mean-square (RMS) speed is a scalar quantity that is calculated by taking the square root of the average of the squared speeds of the individual molecules. As it's an average of the squared speeds, it represents the "typical" speed of a random molecule in a sample of gas.
03

Understanding Average Speed

Average speed is a scalar quantity that is calculated by taking the total distance traveled by an object and dividing it by the total time taken to travel that distance. This gives us the measure of an object's overall rate of motion without considering its direction.
04

Explaining Zero Average Velocity in a Closed Auditorium

In a closed auditorium, air molecules are in constant random motion, colliding with each other and the walls of the auditorium. These random motions in various directions cause the individual velocities of the molecules to cancel each other out. As a result, the sum of their displacements is zero, making their average velocity zero.
05

Explaining Non-Zero Root-Mean-Square Speed and Average Speed

Although the average velocity of air molecules in a closed auditorium is zero, their root-mean-square speed and average speed are not zero because they are scalar quantities and are not affected by the direction of motion. These quantities give information about the magnitude of motion experienced by the molecules in a sample of gas. Since air molecules are in constant random motion, their root-mean-square speed and average speed remain non-zero even though their average velocity is zero.

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Most popular questions from this chapter

At a temperature of \(295 . \mathrm{K},\) the vapor pressure of pentane \(\left(\mathrm{C}_{5} \mathrm{H}_{12}\right)\) is \(60.7 \mathrm{kPa}\). Suppose \(1.000 \mathrm{~g}\) of gaseous pentane is contained in a cylinder with diathermal (thermally conducting) walls and a piston to vary the volume. The initial volume is \(1.000 \mathrm{~L},\) and the piston is moved in slowly, keeping the temperature at \(295 \mathrm{~K}\). At what volume will the first drop of liquid pentane appear?

A closed auditorium of volume \(2.50 \cdot 10^{4} \mathrm{~m}^{3}\) is filled with 2000 people at the beginning of a show, and the air in the space is at a temperature of \(293 \mathrm{~K}\) and a pressure of \(1.013 \cdot 10^{5} \mathrm{~Pa}\). If there were no ventilation, by how much would the temperature of the air rise during the \(2.00-\mathrm{h}\) show if each person metabolizes at a rate of \(70.0 \mathrm{~W} ?\)

1 .00 mol of molecular nitrogen gas expands in volume very quickly, so no heat is exchanged with the environment during the process. If the volume increases from \(1.00 \mathrm{~L}\) to \(1.50 \mathrm{~L},\) determine the work done on the environment if the gas's temperature dropped from \(22.0^{\circ} \mathrm{C}\) to \(18.0^{\circ} \mathrm{C}\). Assume ideal gas behavior.

Compare the average kinetic energy at room temperature of a nitrogen molecule to that of a nitrogen atom. Which has the larger kinetic energy? a) nitrogen atom b) nitrogen molecule c) They have the same energy. d) It depends upon the pressure.

6.00 liters of a monatomic ideal gas, originally at \(400 . \mathrm{K}\) and a pressure of \(3.00 \mathrm{~atm}\) (called state 1 ), undergo the following processes: \(1 \rightarrow 2\) isothermal expansion to \(V_{2}=4 V_{1}\) \(2 \rightarrow 3\) isobaric compression \(3 \rightarrow 1\) adiabatic compression to its original state Find the pressure, volume, and temperature of the gas in states 2 and \(3 .\) How many moles of the gas are there?
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