Questions about the Kinetic Molecular Theory

[September24]

Okay so I'm trying to clarify a couple things about the kinetic molecular theory. It seemed simple but apparently, I don't know it as well as I thought. I apologize in advance for the confusing questions. I'm a bit confused right now.

1. I know that KE=1/2mv^2 but Kinetic Energy=3/2RT
Is the difference that one equation simply applies to gases while the other is for solids/liquids or Does KE=1/2mv^2=3/2RT

2. I wrote down some relationships which I was wondering if people could confirm
Effusion rate is inversely proportional to the square root of mass
Velocity is proportional to the square root of Kinetic Energy
Since Kinetic energy is proportional to temperature, velocity is proportional to square root of Temperature
(This one I'm not so sure)....Velocity is inversely related to square root of mass... (meaning lighter gases move faster, if a gas is two times the mass, it moves 1.4X faster.

3. This is EK1001 number 199 and 200
Q:The average speed of the molecules in a sample of carbon dioxide is found to be the same as the sample of neon. How do the temperatures of the sample compare?

A:The temperature of carbon dioxide is roughly two times the temperature of neon

This i get....Speed is the same for both. However, since CO2 is more massive, it has more KE and more temperature. But this second question mixes things up

Q: The average molecular KE of a sample of CO2 is found to be the same as that of sample of neon. How do the temperatures compare?

A: The temperatures of the two samples are the same?

Looking from KE=3/2RT point of view, it seems simple. However, what about the fact that the masses of the two components are different? How can KE and T be the same if mass is different? Is it because of velocity?

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[shahcoco]

I can't answer your question in terms of the science, but I can answer it partially using test taking skills. Specifically: don't worry about mass in the second question just because it was talked about in the question before. Take every discrete as it's own.

The speed question is more of a physics question than a gen chem question to me, and in physics when you're talking about KE, KE=1/2mv^2. When it says speed, you know you need v. Therefore, you need the KE equation with v.

The second question is more of gen chem question and is asking you to compare the average KE of two gases. It prompts you by mentioning temp and including the word average, so you know you need the KE with temp included. By definition 3/2RT is the average KE of a molecule. Done. Don't worry about mass just because the previous question was talking about it.