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General Chemistry Principles, Patterns, and Applications, 2011

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Root mean square speed<br />

vrms = v21+ v22 + v23+×××+ v2nn - - - - - - - - - - - -Ö<br />

Graham’s law for diffusion <strong>and</strong> effusion<br />

: r1r2 = M2M1- - - Ö<br />

Kinetic molecular theory of gases<br />

vrms = 3RTM - - - -Ö<br />

C O N C E PTUAL P R OBLEMS<br />

1. Which of the following processes represents effusion, <strong>and</strong> which represents diffusion?<br />

a. helium escaping from a hole in a balloon<br />

b. vapor escaping from the surface of a liquid<br />

c. gas escaping through a membrane<br />

2. Which postulate of the kinetic molecular theory of gases most readily explains the observation that a heliumfilled<br />

balloon is round?<br />

3. Why is it relatively easy to compress a gas? How does the compressibility of a gas compare with that of a<br />

liquid? A solid? Why? Which of the postulates of the kinetic molecular theory of gases most readily explains<br />

these observations?<br />

4. What happens to the average kinetic energy of a gas if the rms speed of its particles increases by a factor of<br />

2? How is the rms speed different from the average speed?<br />

5. Which gas—radon or helium—has a higher average kinetic energy at 100°C? Which has a higher average<br />

speed? Why? Which postulate of the kinetic molecular theory of gases most readily supports your answer?<br />

6. What is the relationship between the average speed of a gas particle <strong>and</strong> the temperature of the gas? What<br />

happens to the distribution of molecular speeds if the temperature of a gas is increased? Decreased?<br />

7. Qualitatively explain the relationship between the number of collisions of gas particles with the walls of a<br />

container <strong>and</strong> the pressure of a gas. How does increasing the temperature affect the number of collisions?<br />

8. What happens to the average kinetic energy of a gas at constant temperature if the<br />

a. volume of the gas is increased?<br />

b. pressure of the gas is increased?<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

954

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