Identify a specific topic from Chapter 11 (or from C105 that applies to Chapter 11) that you are having a bit of difficulty with. The next person to respond should address that problem to the best of their ability and then identify their own issue.
So I will start the process off:
"Jane" says that she is having difficulty with understanding why there is 1/8th of a corner atom inside a face-centered cubic unit cell. In response to this, I would explain:
A corner atom of a cubic unit cell is cut through by 3 planes (looking at the pictures in your text, page 521 and 522 will help you to see this as I try to explain). For example, a front plane, a side plane and a top plane. Since this "cuts" the atom in half each time, the first time I throw away 1/2 of the atom, leaving 1/2, the second "cut" throws away 1/2 of 1/2 leaving 1/4 and the third "cut" throws away 1/2 of 1/4 leaving 1/8 inside the cubic unit cell. It does not matter whether it is a primitive cubic unit cell, a face-centered cubic unit cell or a body-centered cubic unit cell, a corner atom will always have 1/8 of the atom inside one cubic unit cell.
A problem that I might have as a student: I don't understand how an increase in the external pressure causes the boiling point to increase.
(Now the next person explain this to me and then list your own issue)
The boiling point of a liquid is defined as the temperature at which the liquid's vapor pressure equals the external pressure. If the external pressure increases it will take more energy or an increase in temperature for the molecules to break apart from their intermolecular forces and for boiling to occur.
ReplyDeleteI have written down in my notes that molecules with the highest boiling point have the lowest vapor pressure. Also I don't understand why with increasing intermolecular forces the vapor pressure decreases.
I think I wrote these down right, but I'm not entirely sure. Explanation of these concepts or correction would be appreciated. Thanks.
You had to choose a hard one but I think i have a good grasp on this topic. I see vapor pressure as the gas released from the liquid and this is a helpful way of thinking of it. If a substance has a high boiling point than it has a hard time evaporating. So it does not release a lot of gas so it will have a low vapor pressure. This kinda of answers both question because boiling point and IMF are directly related. If one goes up the other goes up. But still if you have a liquid with a high IMF that means it will take a lot of energy to make that liquid evaporate, meaning it will have a low vapor pressure. I hope I answered your question correctly and in a manner that makes it a little more simple and easy to understand. (Page 502-503, section 11.5)
ReplyDeleteI have had a bit of trouble understanding surface tension and how top layer of molecules is stronger than the layers under it. I don't quite get how when they are all the same molecules that this one group is stronger than the others.
It is not that the top layer of molecules are stronger, it is that the top layer of molecules have nothing above them to pull on them. The only pull is from the sides and from below. Thus there is a net downward pull on those top molecules providing the surface tension.
DeleteThanks for your responses.
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