vapor pressure and heat of vaporization

[97spooncivic]

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Can anyone help me understand why higher vapor pressure results in a lower heat of vaporization.

Here is the explanation given, but I still don't quite get it.

The vapor pressure of a liquid is the pressure at which vaporization and condensation are at equilibrium. Higher vapor pressure implies weaker intermolecular forces, and, consequently, a lower heat of vaporization.

thanks

 

[PiBond]

Can anyone help me understand why higher vapor pressure results in a lower heat of vaporization.

Here is the explanation given, but I still don't quite get it.

The vapor pressure of a liquid is the pressure at which vaporization and condensation are at equilibrium. Higher vapor pressure implies weaker intermolecular forces, and, consequently, a lower heat of vaporization.

thanks

above every liquid there is a certain bit of vapor pressure formed when molecules at the surface escape. these vapors are composed of gas particles and go between the liquid and gas phase (temporarily exist as a gas and then condense back to a liquid). if you think of heat of vaporization as related to the strength of the intermolecular forces between molecules, then stronger intermolecular forces (a high heat of vap) will result in not that much vapor above the liquid.

a high vapor pressure equates to weak intermolecular forces between molecules (or a high temp resulting in disrupting intermolecular forces) which means more can escape

 

[Insulinshock]

What PiBond said.

95% of all the conceptual problems with vapor pressure, melting point, vaporization, freezing, etc., etc. can be solved by understanding the intermolecular forces of the molecule in question.

Know the forces present then use intuition! IF you think your question through it makes logical sense.

 

[godcyning]

The vapor pressure of a liquid is the pressure at which vaporization and condensation are at equilibrium. Higher vapor pressure implies weaker intermolecular forces, and, consequently, a lower heat of vaporization.

If it helps just think of it as an equilibrium problem: you have the "reaction" (just a physical process here, though):

liquid <=> vapor

This process has some equilibrium associated with it. When it reaches equilibrium, there's a certain amount of vapor, which leads to a "vapor pressure". The forward process has some energy requirement, called the "heat of vaporization", it's the deltaH of the endothermic process.

So if the vapor pressure is higher (lots of vapor), then it means that it's easier to vaporize the liquid (i.e. go forward), so the energy requirement (heat of vap) must be lower.

Why is heat of vap lower? Could be lots of things but the only reason you need to know is that stronger intermolecular forces will cause things to want to be liquid, making it harder to vaporize and therefore making heat of vap higher.

 

[BennieBlanco]

If it helps just think of it as an equilibrium problem: you have the "reaction" (just a physical process here, though):

liquid <=> vapor

This process has some equilibrium associated with it. When it reaches equilibrium, there's a certain amount of vapor, which leads to a "vapor pressure". The forward process has some energy requirement, called the "heat of vaporization", it's the deltaH of the endothermic process.

So if the vapor pressure is higher (lots of vapor), then it means that it's easier to vaporize the liquid (i.e. go forward), so the energy requirement (heat of vap) must be lower.

Why is heat of vap lower? Could be lots of things but the only reason you need to know is that stronger intermolecular forces will cause things to want to be liquid, making it harder to vaporize and therefore making heat of vap higher.

it is the entire FORWARD process (completion). Not just the energy required to move forward...

 

[BennieBlanco]

I find this forum funny.

One person will answer a question. Lets call him guy A.

Then guy B will come around and answer the question and paraphrase.

Then guy C comes along, thinking he too should paraphrase. Rarely do I see the guys B, C, D... add anything. Which makes me wonder if they do it for themselves or the poster (or maybe they don't care to read the earlier responses.

POST: What is 5+5?

Guy A: 10

Guy B: Ten

Guy C: The answer would be like putting two 5's together, which totals 10.

 

[godcyning]

it is the entire FORWARD process (completion). Not just the energy required to move forward...

Right, my bad.

 

[BennieBlanco]

Right, my bad.

No bad. Just wanted to be sure there was clarity.👍

 

[Ibraiz]

I think its actually helpful when people paraphrase, it gives different perspective and different wordings (sometimes easier to understand). People taking time out of their life to help a random stranger, this is very nice of them.

Shout out to all the members of this forum: I really appreciate all the help, time and effort.

Thank you and keep the good job up