Intermolecular forces

[1 lousy student]

I'm new here and my question is with regards to chemistry. Moderators if I posted in the wrong place, please move it to the correct place.

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Can someone please explain to me the concept of intermolecular forces and the effects of intermolecular in:

1. Evaporation

2. Surface tension

3. Solubility

4. Boiling points

5. Capillarity

 

How does intermolecular forces effect these things? I did try a textbook but it wasn't clear and missed some of those points numbered above. I know this is rather easy for most of you guys so please help me understand this as I have failed to grasp the concept.

 

Many thanks

[Elite Engineer]

1.) Evaporation- The strength of intermolecular forces between two molecules govern how fast a solution will change phases if heated. The stronger the IM forces the more energy (heat) it will take to change the solutions phase. An example of this would be water. Water boils at 100 C, because of the maximized hydrogen bonding and polar interactions between the water molecules. On the otherhand, ethanol boils at 78.7 C because it has weaker IM forces.

 

2.) Surface Tension- The strength of the IM forces always governs how well molecules stay bonded/ adjacent to each other. Again, using water as an example, if you fill a cup with water to the very top, you can slightly tilt the cup so the water just barely dips over the edge of the cup, and not spill out. This is because of the very strong IM forces between the water molecules making strong

surface tension.

 

3.) Solubility- Again, depending on how strong IM forces are, a substance will be either easier or more difficult to dissolve. The stronger molecules A and B are attracted to each other, the more difficult it is for solvent C to interact with molecule A.

 

4.) Boiling Points - (see evaporation above)

 

5.) Capillary Action- Same principle as surface tension, except that the fluid is being pulled through a tube/ funnel.

 

Such IM forces that make up these interactions are Hydrogen Bonding, Dipole-Dipole interactions, and London Dispersion forces.

 

~EE

Edited April 10, 2016 by Elite Engineer

[1 lousy student]

@Elite Engineer Thank you so much for that simple yet meaningful explanation. This helped me so much in understanding this a little better.

 

Just one more question: will different substances react differently to surface tension, for example if I had one cup filled with water and another filled with X will it be possible that if both cups were tilted to a sane degree that substance X will drip out and water will remain in the cup?

 

What conclusion can be made about IM and substances ?

Edited April 10, 2016 by 1 lousy student

[Elite Engineer]

@Elite Engineer Thank you so much for that simple yet meaningful explanation. This helped me so much in understanding this a little better.

 

Just one more question: will different substances react differently to surface tension, for example if I had one cup filled with water and another filled with X will it be possible that if both cups were tilted to a sane degree that substance X will drip out and water will remain in the cup?

 

What conclusion can be made about IM and substances ?

depends on what substance "X" is. If "X" is very polar, more so than water then it will not spill out of the cup.

 

Conclusion: Behavior of solutions whether it be evaporation, surface tension, BP, etc is dependent on it's molecular make-up and IM forces.

Edited April 10, 2016 by Elite Engineer

[1 lousy student]

depends on what substance "X" is.

Let's say it's oil or methylated spirits. (Use which ever one you prefer)

[Elite Engineer]

Let's say it's oil or methylated spirits. (Use which ever one you prefer)

Most definitely water will be able to dip at the higher angle w/o spilling out. Oil and methylated spirits have far less stronger IM forces relative to water. However, mewthylated spirits would be able to dip more than oil, due to hydrogen bonds and dipole-dipole interactions via the OH groups. so you could say:

 

Highest surface tension <---------------> Lowest surface tension

 

Water > Methylated spirits > Oil

 

~EE

[1 lousy student]

Most definitely water will be able to dip at the higher angle w/o spilling out. Oil and methylated spirits have far less stronger IM forces relative to water. However, mewthylated spirits would be able to dip more than oil, due to hydrogen bonds and dipole-dipole interactions via the OH groups. so you could say:

 

Highest surface tension <---------------> Lowest surface tension

 

Water > Methylated spirits > Oil

 

~EE

So basically the stronger the IM force, the higher the surface tension?

[Elite Engineer]

So basically the stronger the IM force, the higher the surface tension?

Yup

[1 lousy student]

Yup

Thanks so much for the help, I really appreciate it.

[Elite Engineer]

Thanks so much for the help, I really appreciate it.

an upvote or 2 wouldn't hurt

[1 lousy student]

an upvote or 2 wouldn't hurt

How do I up vote?

[Elite Engineer]

see the the green arrow in the bottom right hand corner of my responses, click that. thx

 

~EE

[1 lousy student]

see the the green arrow in the bottom right hand corner of my responses, click that. thx

 

For some reason only reply is displayed on my side. I will log in from my computer and try again just now.

~EE

[Enthalpy]

For solubility, you have to check the nature of the intermolecular forces (which are not just stronger and weaker), and at both the solvent and the candidate solute.

 

Because a solution or mixture needs to solvent and solute to attract an other, but it also needs to separate some solvent molecules, and possibly some solute molecules if they were a liquid or solid. Thermal energy helps to mix both species but to a limited extent.

 

Many people want to explain capillarity by the mere surface tension, but I suspect that the nature of the intermolecular forces at the liquid and solid, and their compatibility, is impotrant too. Beware non-mainstream paragraph.