asked by @lingjings1 •
almost 2 years ago •
Physics
• 5 pts

What happens to the molecules average velocity?

So, there are two potential answers to this question, because I don't know how precisely the question was written. Part 1 will be if I take this question EXACTLY as it's written, and part 2 will be the answer to this question the way I assume the question was MEANT to be answered.

**PART 1**

In a gas, you have a distribution of **speeds** known as the Maxwell-Boltzmann distribution. There is an average **speed** of the gas that is nonzero, and you can find it using the distribution.

HOWEVER, all **directions** of motion for the gas are equally likely, so even though there is a non-zero average **speed**, the average **velocity** WILL be zero.

So, changing the temperature of the gas has no affect on the average velocity, which will always be zero.

**PART B**

Now, what I think this problem meant for you to do is to relate the average **speed** of the gas to the temperature. This is not zero, as I mentioned above. The equation relating the two is:

v_av = SQRT(8*RT/pi*M)

where R is the ideal gas constant, T is the temperature of the gas, and M is the molar mass of the gas.

In this case, it's clear that if T becomes 2T, then v*av becomes SQRT(2)*v*av, since the average **speed** is proportional to the square-root of the temperature.

If this problem was written by your professor, I would ask him/her what they meant in the problem. If this is for an online homework system like Mastering Physics, I would go with the literal answer, part 1. If that's wrong, then put in the answer for part B.

answered by @doug •
almost 2 years ago

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