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General : covalent bonds and molecular structure
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(1 recommendation so far) Message 1 of 2 in Discussion 
From: diane113  (Original Message)Sent: 8/7/2008 12:33 AM
More pre-test questions:
1. Molecular orbitals extending over more than two atoms provide an explanation for:
a. coordinate covalent bonding
b. ionic bonding
c. paramagnetism
d. resonance
 
My answer: c
 
 
2.At a given temp and pressure, which has the greatest molar entropy?
a. Br2(s)
b. Br2(l)
c. Br2(g)
d. all of these would be expected to have the same moar entropy
 
My answer: c (From largest to smallest, it's always gas > liquid > solid....is this correct?)
 
3. A gas expands into a vacuum (external pressure = 0) while in thermal isolation from the surroundings.  For this expansion
a. ΔE increases
b. ΔE does not change
c. ΔE decreases
d. ΔE=T1S
 
My answer: c (because the work is pushing out of the system, into the surroundings, therefore it is expending energy)
 
 
 


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(1 recommendation so far) Message 2 of 2 in Discussion 
From: MSN Nickname·Steve·Sent: 8/7/2008 1:54 AM
1.  This sounds like the condition for resonance.  When you draw the dot structure of SO2, for example, there are several structures, two of which have octets on all the atoms and with a double bond to one oxygen or to the other:
 
O=S–O      O–S=O
 
Imagine blending these two structures into one, which is what the actual SO2 molecule is (making the S–O bonds equivalent).  In the molecular orbital picture, there will be a molecular orbital made up of the p-orbitals on the sulfur and both oxygens extending over and under the plane of the molecule which includes all three atoms/
 
2.  C is correct.
 
3.  If the gas is expanding into a vacuum, then no work is being done (w = 0).  And if the system is thermally isolated, the heat exchanged between the system and the surroundings is also zero (q = 0).  Therefore, ΔE = q + w  =  0 + 0  =  0, which would be answer B.  Hope that makes sense!
 
 
Steve