Physics 141, Fall 2016.

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Physics 141, Homework Set # 11. Due: 12/13/16, 12 pm (noon).

1.     (50%) WeBWorK set # 11.

 

2.     (25%) In this problem we use the results of measurements of the temperature dependence of the heat capacity of Hydrogen gas (H2) at constant volume to determine the molecular properties of Hydrogen.

a.     At temperatures below 80 K the heat capacity (at constant volume) is (3/2)k per molecule, but at higher temperatures the heat capacity increases to (5/2)k per molecule due to contributions from rotational energy states.  Use these observations to estimate the distance between the hydrogen nuclei in an H2 molecule.

b.     At about 2000 K the heat capacity (at constant volume) increases to (7/2)k per molecule due to contributions from vibrational energy states.  Use these observations to estimate the stiffness of the "spring" that approximately represents the inter-atomic force.

 

3.     (25%) A rigid, thermally insulated container with a volume of 22.4 liters is filled with one mole of helium gas (4 grams per mole) at a temperature of 0 Celsius (273 K).  The container is sitting in a room, surrounded by air at standard temperature and pressure (STP: 1 atmosphere and 0 Celsius).

a.     Calculate the pressure inside the container in N/m2.

b.     Calculate the root-mean-square speed of the helium atoms.

c.     Now open a tiny square hole in the container, with area 10-8 m2.  After 5 seconds, how many helium atoms will have left the container?

d.     During the same 5 seconds, some air molecules from the room will enter the container through the same hole.  How many air molecules will enter the container?

e.     Does the pressure inside the container increase or decrease during this 5 seconds period?

Last updated on Monday, September 26, 2016 8:41

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