CH301 2010 Worksheet 9 on Gases
1. What are the assumptions of Kinetic Molecular Theory?
Answer: Gases have no volume (infinitely small), gas molecules do not interact with one another (no attractions
or repulsions). As a result, they collide elastically (no energy is lost).
2. For the following variable pairs, tell if they have directly proportional or inversely proportional relationships:
a. V & T
b. P & T
c. n & P
d. P & V
Answer: a. proportional , b. proportional, c. proportional, d. inverse. These can be figured out by looking at the
ideal gas law, PV = nRT.
3. The ideal gas law can be used to solve for the molecular weight of an unknown gas. If 1 g of a hypothetical
molecule at STP takes up 1 L of volume, what is the molecular weight of that molecule?
Answer: We can use the ideal gas law here, substituting using n = m/M where m is mass and M is molecular
weight. Solving for M, we find M = mRT/PV. Plugging in, M = (1 g * 0.0821 L atm per mole per K * 273 K /
(1 atm * 1 L) = 22.4 g/mol
4. You should know that many gases do not behave ideally and therefore do not obey the ideal gas law. How do
we correct for this in real life calculations when we need more accurate answers?
Answer: Real gases can still be approximated by the ideal gas law. To improve the accuracy of our calculations,
we can add corrections or “fudge factors”. Probably the most common example of this is the Vanderwaal’s
equation, which has a form similar to the ideal gas law but with adjustments to the P and V terms.
5. Describe the relationship between diffusion, effusion, and gas speed.
Answer: They are all proportional. Higher gas speeds lead to higher diffusion rates and higher effusion rates.
6. If two gas molecules have the same kinetic energy, which will move faster, the larger molecule or the smaller
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 Fall '10
 Laude
 Molecule, Kinetic theory

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