Melting pt, freezing pt, boiling point

[Dr.9999]

Can someone please explain the rules for mp,fp and bp? I'm confused between freezing and melting point. Is it melting point that has the same rule as boiling point? I know high boiling points have to do with hydrogen bonding, the length and the size of the carbon chain etc...But I get confused when they ask which of the following has the highest bp, mp, and fp. Or which of the following has the lowest mp, bp, and fp.
Thanks!

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[412smb412]

Can someone please explain the rules for mp,fp and bp? I'm confused between freezing and melting point. Is it melting point that has the same rule as boiling point? I know high boiling points have to do with hydrogen bonding, the length and the size of the carbon chain etc...But I get confused when they ask which of the following has the highest bp, mp, and fp. Or which of the following has the lowest mp, bp, and fp.
Thanks!

high bp = most stable. if u have alkanes that are constitutional isomers, the one with the least branching has the highest bp, but for mp/ freezing you are concerned about which can pack easier, the one that has 'less space' or more branching will take up less space and therefore is easier to pack and will have a higher mp

 

[Dr.9999]

2 moles of the following solutes is added to 1L of pure water. Which of the five ensuing solutions would have the lowest freezing point?

a) 2 NaCl
b) .4 CaCl2
c) .1KCl
d) 3 NaI
e) .02 KI

2x2= 4
.4x3= 1.2
.1x2=.2
3x2=6
.02x2= .04

I got this far but I don't know what to do after here. The smallest is .2 and the largest is 6 so which one has the lowest freezing point?
What if they asked which one has the lowest melting point or highest freezing point?

 

[YYC]

For any substance, the melting point and freezing point are the same (same value). The difference is that melting point is used to describe the temperature at which the solid becomes a liquid and the freezing point is used to describe the temperature at which a liquid becomes a solid.

But remember, at either the melting or freezing point exactly, both the solid state and liquid state of the substance coexist. Same goes to boiling point.

If asked which has highest boiling point, like you said, substance with stronger intermoleculer forces tends to have the higher boiling point. network covalent (i.e. dimond) > ionic > H-bonding > dipole-dipole > london dispersion.

If asked which has highest melting/freezing point, substance with stronger intermolecular forces tend to have higher meltingfreezing point. same with boiling point.

some special rules to know too:

-substances that are more branched in their molecular structure tends to have a higher melting/freezing point and lower boiling point than the substances that are straight up just chains. (ex. isobutane vs. butane).

-if you add more soluble solutes into a liquid, you are going to decrease its melting/freezing point and increase its boiling point. (commonly known as the freezing-point depression and boiling point elevation). an example would be why people add salts on frozen roads to melt the ice for the salt mixes with the water and lowers its freezing point.

 

[Dr.9999]

Thanks!
So if they were to ask which of the following has the lowest melting point, it would have been the same answer as the lowest freezing point. Right? Also the answer to that question is 6 so the largest solutions would have the lowest fp and the smallest would have the highest fp. Let me know if I'm on the right track.

 

[YYC]

the answer is indeed 6. the solute that yields the most number of aqueous ions in the solution will affect the freezing/melting point the most. in this case, the one with n=6 also have the highest boiling point.