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Chemistry Forums for Students => High School Chemistry Forum => Chemistry Olympiad and other competitions => Topic started by: T on July 18, 2015, 06:37:56 PM

Title: Vapour pressure
Post by: T on July 18, 2015, 06:37:56 PM

Hello,

The question is:

Butane has a vapour pressure of 47.156 kPa at 253 K, and 149.03 kPa at 283 K. Is butane gaseous or non-gaseous under the following conditions:

Temp. = 253 K      Pressure = 1 atm
Temp. = 253 K      Pressure = 2 atm
Temp. = 283 K      Pressure = 1 atm
Temp. = 283 K      Pressure = 2 atm

So firstly, I have searched what vapour pressure means. And from what I read, vapour pressure is the pressure of the vapour of a liquid at equilibrium in a closed system. And can only affected by temperature.

So since butane has a vapour pressure of 47.156 kPa at 253 K, at 253 K and 1 atm the vapour pressure of butane would still be 47.156 kPa. However, I am not sure how the external pressure would affect the physical state of butane. Could someone explain this? Also does the 1 atm mean that in a closed system, the pressure in it is 1 atm?

Thanks

Title: Re: Vapour pressure
Post by: mjc123 on July 18, 2015, 06:44:25 PM

What happens when the vapour pressure of a liquid is greater than the external pressure?

Title: Re: Vapour pressure
Post by: T on July 18, 2015, 07:00:45 PM

The liquid boils doesn't it?

So when butane has:
Temp. = 283 K      Pressure = 1 atm
It would be gaseous?

And for the others it would be non-gaseous?

Title: Re: Vapour pressure
Post by: mjc123 on July 19, 2015, 05:34:49 PM

Correct

Title: Re: Vapour pressure
Post by: T on July 20, 2015, 05:09:42 AM

Thanks mjc123