orgo and gen chem questions

[yankeefan86]

---

Members don't see this ad.

These questions are from the 2009 sample paid DAT test. Can someone help explain these two?
55. Which of the following is produced by the electrolysis of 18g of h2O?
A) 1 mol O2
B) 2 mol of O2
C) 1 mol of H2
D) 2 mol of H2
E) 1/2 mol of H2.

the answer is C. I understand why its C but couldn't it also be A as well?

74. Which of the following compounds is the most thermodynamically stable?

A) blank( there was no answer choice here looks like the ADA forgot to put it in)
B) ch2=C=CHCH2CH2CH3
C) CH3CH2CH=C=CHCH3
D) CH3CH=CHCH=CHCH3
e) Ch2=ChCH2Ch=CHCH3

the answer is D.

 

[shdwpally]

Well A should be 1/2 mol O2 I believe for it to be right.

And ochem the answer is a conjugated diene, making it the most stable and thermodynamically favorable because of resonance

 

[bharat008]

These questions are from the 2009 sample paid DAT test. Can someone help explain these two?
55. Which of the following is produced by the electrolysis of 18g of h2O?
A) 1 mol O2
B) 2 mol of O2
C) 1 mol of H2
D) 2 mol of H2
E) 1/2 mol of H2.

the answer is D. I understand why its D but couldn't it also be A as well?

74. Which of the following compounds is the most thermodynamically stable?

A) blank( there was no answer choice here looks like the ADA forgot to put it in)
B) ch2=C=CHCH2CH2CH3
C) CH3CH2CH=C=CHCH3
D) CH3CH=CHCH=CHCH3
e) Ch2=ChCH2Ch=CHCH3

the answer is D.

First one, I don't like that question. It should have said 2 mol of H, not 2 mol of H2 b/c that would make it 4 mol at the end.

Second one, i hope u know that there are 2 kinds of conjugated diene systems - conjugated and cumulated. Conjugated is more stable and has low heat of hydrogenation compared to cumulated diene.

Conjugated dienes are two double bonds separated by a single bond
Cumulated Dienes are two double bond connected to a similar atom

Look at the diagram below showing the heats of hydrogenation for conjugated dienes:::
http://chemwiki.ucdavis.edu/Organic...ugated_vs._Nonconjugated_vs._Cumulated_Dienes

 

[herkulease]

1st one seems odd

the balance equation is

2H2O -> 2H2 + O2

If you have 18grams of H2O then you have 1 mol of H2O

So

1 mol of H2O X 2 mols H2/2 mol H2O = 1 mol of H2

or

1 mol of H2O X 1 mols O2/2 mol H2O = 1/2 mol O2

I don't see how as you said they have D as the correct choice. Of the choices only C is valid.

I remember someone saying there was supposed to be a corrections handout sheet. But some people would get them while others didn't. Search the forums perhaps.

 

[yankeefan86]

1st one seems odd

the balance equation is

2H2O -> 2H2 + O2

If you have 18grams of H2O then you have 1 mol of H2O

So

1 mol of H2O X 2 mols H2/2 mol H2O = 1 mol of H2

or

1 mol of H2O X 1 mols O2/2 mol H2O = 1/2 mol O2

I don't see how as you said they have D as the correct choice. Of the choices only C is valid.

I remember someone saying there was supposed to be a corrections handout sheet. But some people would get them while others didn't. Search the forums perhaps.

the answer is C, I looked at it wrong, my bad. Thank guys for the feedback!