Boiling Point

[llungu]

---

Members do not see this ad.

I have a quick question about boiling point from Kaplan.. They say that cis isomer of butene has a higher melting point... I think trans does because it is symmetrical and packs better in the solid state. Am I right?

Also

Which of the following has the highest melting point?
A. trans - 2 butene
B. cis - 2 - butene
C. n-butane
D. 1-propanol
E. 1- pentanol

Are hydrogen bonds also important for melting point? I wasn't sure if it was important only for boiling point..

Thanks!

 

[nze82]

I have a quick question about boiling point from Kaplan.. They say that cis isomer of butene has a higher melting point... I think trans does because it is symmetrical and packs better in the solid state. Am I right?
Boiling point has nothing to do with symmetry and the packing ability of molecules (These determine melting points). Boiling point has to do with the intermolecular interactions. Cis isomers have greater intermolecular interactions, because they have a net dipole moment (Trans isomers don't, because the dipole moments cancel out).

Also

Which of the following has the highest melting point?
A. trans - 2 butene
B. cis - 2 - butene
C. n-butane
D. 1-propanol
E. 1- pentanol

Are hydrogen bonds also important for melting point? I wasn't sure if it was important only for boiling point..
I believe they do. Melting point determines the temperature that enough intermolecular forces are broken apart, so that the substance changes from solid to liquid. The stronger these intermolecular forces, the more energy needs to be spent to break them apart, which means the higher the temperature will become. So, I think (E) is the correct answer, because it's the largest molecule and it's capable of hydrogen bonding (I might be wrong. Double check this).

Thanks!

Good Luck👍

 

[llungu]

Sorry I meant to say melting point in that first sentence... But your explanation answered my question.. Trans has higher melting point, and cis has higher boiling point.

And E is the correct answer for the bottom one! For the reasons you stated.

 

[anteater85]

easiest way to find which has the highest bp is just draw the structure of each molecule in ur mind and count the number of hydrogen. The one with the highest number of hydrogens has a higher bp.