Midterm 2011 2B

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Julia Kim 1D
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Joined: Fri Sep 25, 2015 3:00 am

Midterm 2011 2B

Postby Julia Kim 1D » Sat Feb 06, 2016 5:38 pm

The question states that
Container A: 1 mol of ideal monatomic gas
Container B: 1 mol of diatomic gas, not vibrationally active
Container C: 1 mol of diatomic gas, vibrationally active.

The answer states that the containers, in order of increasing change in entropy is B<C<A

Why is A the greatest. I could understand that maybe since A is smaller and lighter, it would move around more creating more entropy, but the answer states that it is because it has a larger number of particles than B or C. But if they are all one mole, don't they have the same number of particles?

Can someone explain why A is the greatest?

Jonathan Shih 3H
Posts: 37
Joined: Fri Sep 25, 2015 3:00 am

Re: Midterm 2011 2B

Postby Jonathan Shih 3H » Sat Feb 06, 2016 8:05 pm

Hey! My TA actually warned me about this earlier and I think I can help!

Basically, the problem is being tricky here, where it is stating that there is 1mol of the element, and that element is in the form of a monatomic or diatomic gas. This means that for the diatomic gas, there are essentially half the number of particles in the container and thus much less entropy.

As for the difference between B and C, I think the entropy difference is pretty obvious based on the difference between one that is vibrationally active versus one that is not vibrationally active.

I personally don't think it's a greate question and should probably be written in a way that's more clear, but I'm pretty sure that's what the answer is supposed to be. Hope this helps!
Last edited by Jonathan Shih 3H on Sat Feb 06, 2016 8:09 pm, edited 1 time in total.

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Re: Midterm 2011 2B

Postby Viktor2E » Sat Feb 06, 2016 8:07 pm

The question specifies that the one mol refers to the amount of atoms not molecules. In the diatomic gas, these atoms are bound together to make half a mol of gas molecules. In the monoatomic gas, the atoms are free. That is why the monoatomic gas has more particles.

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