[dtbcn]

1. rationalizing the difference in boiling point for CH3CH2CH3 (-42 C) and CH3OCH3 (-25 C)

I think i got this figured out but I'm not sure.

Propane is non polar and experiences London dispersion force and dimethyl ether is polar and experiences dipole-dipole force. Dipole forces are stronger making the boiling point higher.

I'm not sure whether dimethyl ether is polar or non polar so that is what confuses me. At first I thought both were non polar but the number of electrons would the same so wouldn't that mean the boiling point should be the same if it was true?

2. How do the following physical properties depend on the strength of intermolecular forces?

a. surface tension
b. viscosity
c. melting point
d. boiling point
e. vapor pressure

Wouldn't the surface tension, viscosity, and boiling point be higher if the intermolecular force is stronger?

I'm really confused about melting point and vapor pressure. If someone could think of an example so I understand better, that would be great. I think that both of them would be higher as the force is weaker but it's just a wild guess.

3. I know that for finding the substance with the highest boiling point, I would have to find the one with the highest intermolecular force. What should I do to find the substance with the highest/lowest freezing point and vapor pressure?

4. I have no idea what to do for this one.

Out of I2, CsBr, CaO, Which has the smallest enthalpy of fusion.
Could someone explain what enthalpy of fusion is? Is it the same as melting point?

Any help would be greatly appreciated.

[Yggdrasil]

1. rationalizing the difference in boiling point for CH3CH2CH3 (-42 C) and CH3OCH3 (-25 C)

I think i got this figured out but I'm not sure.

Propane is non polar and experiences London dispersion force and dimethyl ether is polar and experiences dipole-dipole force. Dipole forces are stronger making the boiling point higher.

I'm not sure whether dimethyl ether is polar or non polar so that is what confuses me. At first I thought both were non polar but the number of electrons would the same so wouldn't that mean the boiling point should be the same if it was true?

Your explanation is correct.  Polarity has nothing to do with the number of electrons.  Polarity has to do with dipoles (which result from bonds between atoms with unequal electronegativities, such as carbon and oxygen). 

2. How do the following physical properties depend on the strength of intermolecular forces?

a. surface tension
b. viscosity
c. melting point
d. boiling point
e. vapor pressure

Wouldn't the surface tension, viscosity, and boiling point be higher if the intermolecular force is stronger?

Correct.

I'm really confused about melting point and vapor pressure. If someone could think of an example so I understand better, that would be great. I think that both of them would be higher as the force is weaker but it's just a wild guess.

Melting point is just like boiling point, because both are examples of a phase transition.  For vapor pressure think of it in terms of boiling point.  The boiling point of a compound is the temperature at which the vapor pressure of your liquid equals the atmospheric pressure.  So, substances with low boiling points will have higher vapor pressures than substances with higher boiling points.

3. I know that for finding the substance with the highest boiling point, I would have to find the one with the highest intermolecular force. What should I do to find the substance with the highest/lowest freezing point and vapor pressure?

See above.

4. I have no idea what to do for this one.

Out of I2, CsBr, CaO, Which has the smallest enthalpy of fusion.
Could someone explain what enthalpy of fusion is? Is it the same as melting point?

Enthalpy of fusion is the energy needed to melt the compound (i.e. to partially break the intermolecular bonds that order the atoms in a crystaline lattice).

[dtbcn]

Thanks. It makes a lot more sense to me now .