vapor pressure question giving me problems...help?

[TexasOMFS]

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Increasing the amount of liquid in a sealed container will cause the vapor pressure of the liquid to
A. Increase, regardless of the identity of the liquid
B. Increase, if the liquid is sufficiently volatile
C. Decrease, regardless of the identity of the liquid
D. Remain the same, regardless of the identity of the liquid
E. Decrease, if the liquid is sufficiently volatile
According to my Kaplan book (2002 edition) the answer is D. Their answer explanation is "In this question, the only thing that is changing is the amount of liquid in the container; this will have no effect on the ability of liquid molecules to become gas molecules." I would've thought that increasing the amount of liquid would decrease the volume that the gas particles can reside in, thus resulting in increased vapor pressure. Someone explain this to me?

 

[wantVCUdental]

Increasing the amount of liquid in a sealed container will cause the vapor pressure of the liquid to
A. Increase, regardless of the identity of the liquid
B. Increase, if the liquid is sufficiently volatile
C. Decrease, regardless of the identity of the liquid
D. Remain the same, regardless of the identity of the liquid
E. Decrease, if the liquid is sufficiently volatile
According to my Kaplan book (2002 edition) the answer is D. Their answer explanation is "In this question, the only thing that is changing is the amount of liquid in the container; this will have no effect on the ability of liquid molecules to become gas molecules." I would've thought that increasing the amount of liquid would decrease the volume that the gas particles can reside in, thus resulting in increased vapor pressure. Someone explain this to me?

Hi TexasOMFS, intuitively, the answer would be increase in vapor pressure. BUT! what the question is REALLY asking you is, what is Kvap when you add more solution to the container.
K, regardless of what it measures, it could be Ksp, Kvap or Kpresure, they all only change when temperature change. Therefore in this situation, since there is no temperature/heat change, the vapor pressure remains constant.

 

[UCB05]

Hi TexasOMFS, intuitively, the answer would be increase in vapor pressure. BUT! what the question is REALLY asking you is, what is Kvap when you add more solution to the container.
K, regardless of what it measures, it could be Ksp, Kvap or Kpresure, they all only change when temperature change. Therefore in this situation, since there is no temperature/heat change, the vapor pressure remains constant.

Also, the reason why vapor pressure remains the same is that because the gas and liquid phases are in equilibrium, if you increase liquid volume and decrease gas volume, molecules in the gas phase will enter the liquid phase without an overall change in pressure.

 

[TexasOMFS]

thanks guys!
VCU seems like u got all the answers! 😛

 

[wantVCUdental]

thanks guys!
VCU seems like u got all the answers! 😛

😀, but my lack of diligence costed me my 30 in both chems on DAT 🙁

 

[TexasOMFS]

Got more questions so I figured I'd just revive my old thread.
1. When talking about SN1, E1 I know it's pretty unusual for a primary carbocation to form unless it's allylic or benzylic resonance stabilized. However is it possible to form a primary carbocation if the cation has the ability to undergo a 1,2-hydride or alkyl shift (which occurs almost immediately after formation of the cation)?
2. Another cation rearrangement question. Usually there's a lot of competition between SN1, E1 products so is it possible that a rearrangement could lead to the + charge being on an alpha carbon where there is no E1 possible (due to no B hydrogens)?
I know these are a bit nitpicky but that's the way I am 😛
Thanks!

 

[AmpedUp]

Got more questions so I figured I'd just revive my old thread.
1. When talking about SN1, E1 I know it's pretty unusual for a primary carbocation to form unless it's allylic or benzylic resonance stabilized. However is it possible to form a primary carbocation if the cation has the ability to undergo a 1,2-hydride or alkyl shift (which occurs almost immediately after formation of the cation)?
2. Another cation rearrangement question. Usually there's a lot of competition between SN1, E1 products so is it possible that a rearrangement could lead to the + charge being on an alpha carbon where there is no E1 possible (due to no B hydrogens)?
I know these are a bit nitpicky but that's the way I am 😛
Thanks!

1) The hydride shift would occur first before anything to form a secondary or tertiary (most common) carbocation...then SN1, E1. That's really that...and it stays this way unless the product is reversed back to its reactant form and you react it with another reagent to make something different.
2) Good question. Not sure.

 

[wantVCUdental]

2. Another cation rearrangement question. Usually there's a lot of competition between SN1, E1 products so is it possible that a rearrangement could lead to the + charge being on an alpha carbon where there is no E1 possible (due to no B hydrogens)?
I know these are a bit nitpicky but that's the way I am 😛
Thanks!

Hi TexasOMFS, in this question, do you mean the plus charge moving from a primary to a secondary carbon?
Because in orgo, when we speak of alpha, beta, it usually is talking about carbonyl groups.
If you are talking about the alpha carbon beside a carbonyl, you can't form the positive charge because the electron in the alpha hydrogen is in resonance with the oxygen of the carbonyl group.
If you are talking about moving from a terminal carbon to a secondary carbon due to hydrogen shift, then you get E1, and the E1 is the predominant reaction, because a carbocation prefers a secondary carbon more than a primary carbon.
Hope this helps.

 

[TexasOMFS]

Thanks a bunch Amped. In Chad's O Chem videos he doesn't give any examples of primary carbocations rearranging to secondary or tertiary. He only gives examples of secondary carbocations rearranging to yield tertiary. So just to make sure I'm understanding everything correctly: the only two cases (that we need to know) where primary carbocations can form are when the cation is allylic or benzylic and when the cation can rearrange to yield a secondary or tertiary carbocation, correct?

 

[TexasOMFS]

Hi TexasOMFS, in this question, do you mean the plus charge moving from a primary to a secondary carbon?
Because in orgo, when we speak of alpha, beta, it usually is talking about carbonyl groups.
If you are talking about the alpha carbon beside a carbonyl, you can't form the positive charge because the electron in the alpha hydrogen is in resonance with the oxygen of the carbonyl group.
If you are talking about moving from a terminal carbon to a secondary carbon due to hydrogen shift, then you get E1, and the E1 is the predominant reaction, because a carbocation prefers a secondary carbon more than a primary carbon.
Hope this helps.

Sorry I should've been more clear. What I meant by alpha was the carbon that originally was attached to the halide and therefore gained a positive charge when it lost the halide (as E1 mechanisms go). By beta I just meant any adjacent carbons that have hydrogens they can lose to form the alkene. However my question here was, after the carbocation forms is it ever possible that it could rearrange to a spot with no adjacent carbons that have hydrogens attached? Thus alkene formation would not occur and the reaction would go primarily by Sn1?