3F.5  [ENDORSED]

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Letty Liu 2C
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Joined: Fri Aug 09, 2019 12:16 am

3F.5

Postby Letty Liu 2C » Mon Nov 11, 2019 7:27 pm

Suggest, giving reasons, which substance in each of the following pairs is likely to have the higher normal melting point (Lewis structures may help your arguments): (a) HCl or NaCl; (b) C2H5OC2H5 (diethyl ether) or C4H9OH (butanol); (c) CHI3 or CHF3; (d) C2H4 or CH3OH.

Can someone explain how we should approach this question? Also, do molecules with more electrons and stronger intermolecular forces have higher melting points?

Andrew Pfeiffer 2E
Posts: 79
Joined: Sat Sep 28, 2019 12:16 am

Re: 3F.5  [ENDORSED]

Postby Andrew Pfeiffer 2E » Mon Nov 11, 2019 7:46 pm

For this type of question, you're going to want to first draw out the Lewis structures of the molecules in the problem. Using the lecture content from this last week, you will determine which intermolecular force applies to the molecules in the question (London dispersion, hydrogen bonding, etc.). And finally, you need to determine the relative melting points. In general, the molecules with stronger intermolecular interactions will have higher melting points than those with weaker intermolecular forces. Hope this helped!

Julie Park 1G
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Joined: Thu Jul 25, 2019 12:15 am

Re: 3F.5

Postby Julie Park 1G » Tue Nov 12, 2019 12:38 am

Looking at the lewis structures may help, and examining the general types of the compound might further clarify which substance has a higher melting point.
For example, in (a), between HCl and NaCl, NaCl will have a higher melting point because it's an ionic compound.
In (b), Butanol is stronger because it has hydrogen bonding (which doesn't exist in diethyl ether).

Knowing the general order of strengths in different kinds of bonds will help you determine relative melting points (stronger the bond, likely higher melting point)

Lauren Tanaka 1A
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Joined: Sat Aug 17, 2019 12:18 am

Re: 3F.5

Postby Lauren Tanaka 1A » Tue Nov 12, 2019 5:43 pm

By drawing the Lewis Structure of each molecule you are then able to determine the type of intermolecular forces in each molecule. The molecules with stronger intermolecular interactions will then have a higher melting point than those molecules that are weaker.

AChoudhry_1L
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Joined: Sat Sep 07, 2019 12:17 am

Re: 3F.5

Postby AChoudhry_1L » Wed Nov 13, 2019 9:05 am

julieepark wrote:Looking at the lewis structures may help, and examining the general types of the compound might further clarify which substance has a higher melting point.
For example, in (a), between HCl and NaCl, NaCl will have a higher melting point because it's an ionic compound.
In (b), Butanol is stronger because it has hydrogen bonding (which doesn't exist in diethyl ether).

Knowing the general order of strengths in different kinds of bonds will help you determine relative melting points (stronger the bond, likely higher melting point)

Don't both structures have hydrogen bonding? If one structure has MORE hydrogen bonding than another, does that mean it would also have a higher boiling point?


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