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Topic: Vapour pressure and boiling point of a liquid  (Read 11575 times)

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Offline curiouscat

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Re: Vapour pressure and boiling point of a liquid
« Reply #15 on: May 09, 2013, 12:17:46 AM »


What do you mean by overcome? Because as you mentioned the presences of other gases doesn't change the vapour pressure. So why would the vapour pressure be the one doing work against the atmosphere?



I was eavesdropping on this discussion and I can't help thinking that you are moving in circles...

Offline Needaask

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Re: Vapour pressure and boiling point of a liquid
« Reply #16 on: May 09, 2013, 08:27:31 AM »


What do you mean by overcome? Because as you mentioned the presences of other gases doesn't change the vapour pressure. So why would the vapour pressure be the one doing work against the atmosphere?



I was eavesdropping on this discussion and I can't help thinking that you are moving in circles...

Haha sorry about that. So what I got now is the vapour isn't really dependent on the surroundings. So when my temperature is high enough it can push the atmosphere back?

Is this correct?

Offline curiouscat

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Re: Vapour pressure and boiling point of a liquid
« Reply #17 on: May 09, 2013, 08:47:16 AM »


What do you mean by overcome? Because as you mentioned the presences of other gases doesn't change the vapour pressure. So why would the vapour pressure be the one doing work against the atmosphere?



I was eavesdropping on this discussion and I can't help thinking that you are moving in circles...

Haha sorry about that. So what I got now is the vapour isn't really dependent on the surroundings. So when my temperature is high enough it can push the atmosphere back?

Is this correct?

Nope. Boiling Points increase with pressure. Ergo if your surroundings are high enough pressure it wont boil till a much higher Temperature is reached.

Offline Needaask

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Re: Vapour pressure and boiling point of a liquid
« Reply #18 on: May 09, 2013, 10:45:45 AM »


What do you mean by overcome? Because as you mentioned the presences of other gases doesn't change the vapour pressure. So why would the vapour pressure be the one doing work against the atmosphere?



I was eavesdropping on this discussion and I can't help thinking that you are moving in circles...

Haha sorry about that. So what I got now is the vapour isn't really dependent on the surroundings. So when my temperature is high enough it can push the atmosphere back?

Is this correct?

Nope. Boiling Points increase with pressure. Ergo if your surroundings are high enough pressure it wont boil till a much higher Temperature is reached.

Oh I thought boiling occurred when VP=surrounding pressure? So having a higher VP meant the boiling point would be lower?

Offline DrCMS

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Re: Vapour pressure and boiling point of a liquid
« Reply #19 on: May 09, 2013, 12:16:01 PM »
This thread is getting to be silly.

The vapour pressure of a particular substance changes with temperature.  The boiling point is visibly reached when the vapour pressure equals the external pressure.

So VP is dependant on T while BP is dependant on P.

If for a particular substance say water in an open beaker you increase the temperature the vapour pressure also increases. 
When the VP reaches the atmospheric pressure you will see bubbles forming in the liquid and we call that boiling - for water at 1 atmosphere the boiling temperature is 100°C
If you put the water in a sealed system and decrease the pressure in the system the water will boil at less than 100°C.
If you put the water in a sealed system and increase the pressure in the system the water will boil at more than 100°C
The vapour pressure of the water in each system at the same temperature will be the same.

Offline curiouscat

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Re: Vapour pressure and boiling point of a liquid
« Reply #20 on: May 09, 2013, 12:19:35 PM »
This thread is getting to be silly.

I agree!

Offline curiouscat

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Re: Vapour pressure and boiling point of a liquid
« Reply #21 on: May 09, 2013, 12:22:02 PM »

 So having a higher VP meant the boiling point would be lower?


Yes.

But having a high ambient pressure  will mean boiling point will be higher.

Ambient pressure and vapor pressure are two different things. Adjectives are important.

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