4 gchem qs

[gomawum]

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1. CH2Cl2 vs. CH@Br2

which one is more polar molecules.

I woul think that since Br is bigger, it is more polarizable (like the Br is better leaving group than Cl in substitution reaction in ochem), but somehow I get this sense that since Cl is more Electronegative than Br, it might be more polarizable, which one sounds more right?



2. F-R2H vs. H2O

which one is more polar (which one has stronger hydrogen bond?)

I know that H-bond is strong in F>O>N, but I see F has only one hydrogen bond while O has 2 hydrogen bond, so which one has significant H-bond?


3. is it ALWAYS true that heat of vaporizaiton is greater than heat of fusion?

I thoguth heat of vaporization(or fusion) is latent heat, so whichever has long plateu line has greater heat of vaporization or fusion,

but one of kaplan question show that heat of vaporization has shorter plateu(---) than heat of fusion(longer, ---------), but heat of vaporization was greater tha heat of fusion.

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4. (same question from above) what is heat capacity in the graph?

 

[rose786]

1. has to do with electronegativities. Cl>Br

2. Take a look again at FR2H. There is no H bonded to the F, (F is bonded to R) therefore there is no H bonding in this molecule.

3. Heat vap > Heat fusion because more intermolecular forces must be overcome in vaporization than in melting.

Don't know which graph you're refering to, sorry.

 

[gomawum]

CH2
|
F - H
|
CH2

has H-bond