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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Calicum on June 08, 2012, 03:11:10 AM

Title: What is the vapor pressure inside a pressure cooker when the temperature is 112C
Post by: Calicum on June 08, 2012, 03:11:10 AM: I know the formula is ln(p1/p2) = ΔHvap/R (1/T2 - 1/T1) but I keep getting the answer wrong.

So far I got:

p1=1
p2=???
T1=373K
T2=385K
ΔHvap=40.65
R=0.0082
Title: Re: What is the vapor pressure inside a pressure cooker when the temperature is 112C
Post by: sjb on June 08, 2012, 03:44:13 AM: Quote from: Calicum on June 08, 2012, 03:11:10 AM
I know the formula is ln(p1/p2) = ΔHvap/R (1/T2 - 1/T1) but I keep getting the answer wrong.

So far I got:

p1=1
p2=???
T1=373K
T2=385K
ΔHvap=40.65
R=0.0082

What are your units for R?
Title: Re: What is the vapor pressure inside a pressure cooker when the temperature is 112C
Post by: Calicum on June 08, 2012, 12:34:09 PM: Quote from: sjb on June 08, 2012, 03:44:13 AM
Quote from: Calicum on June 08, 2012, 03:11:10 AM
I know the formula is ln(p1/p2) = ΔHvap/R (1/T2 - 1/T1) but I keep getting the answer wrong.

So far I got:

p1=1
p2=???
T1=373K
T2=385K
ΔHvap=40.65
R=0.0082

ΔHvap=40.65 KJ/mol
R=0.0082 KJ/mol K

What are your units for R?
Title: Re: What is the vapor pressure inside a pressure cooker when the temperature is 112C
Post by: Calicum on June 08, 2012, 01:48:07 PM: Nvm I got my answer. ;D
Title: Re: What is the vapor pressure inside a pressure cooker when the temperature is 112C
Post by: JonG on June 08, 2012, 10:17:49 PM: R should equal 8.314 J/K mol
Title: Re: What is the vapor pressure inside a pressure cooker when the temperature is 112C
Post by: Calicum on June 09, 2012, 01:57:44 AM: Quote from: JonG on June 08, 2012, 10:17:49 PM
R should equal 8.314 J/K mol

??? ???

Since my ΔHvap is in KJ/mol it would make sense to change R into KJ/mol too. I do not understand what you mean.
Title: Re: What is the vapor pressure inside a pressure cooker when the temperature is 112C
Post by: Borek on June 09, 2012, 02:56:44 AM: Quote from: Calicum on June 09, 2012, 01:57:44 AM
Quote from: JonG on June 08, 2012, 10:17:49 PM
R should equal 8.314 J/K mol

??? ???

Since my ΔHvap is in KJ/mol it would make sense to change R into KJ/mol too. I do not understand what you mean.

If you used R equal to 0.082 your units were L atm K^-1 mol^-1.
Title: Re: What is the vapor pressure inside a pressure cooker when the temperature is 112C
Post by: Calicum on June 09, 2012, 06:30:33 AM: Quote from: Borek on June 09, 2012, 02:56:44 AM
Quote from: Calicum on June 09, 2012, 01:57:44 AM
Quote from: JonG on June 08, 2012, 10:17:49 PM
R should equal 8.314 J/K mol

??? ???

Since my ΔHvap is in KJ/mol it would make sense to change R into KJ/mol too. I do not understand what you mean.

If you used R equal to 0.082 your units were L atm K^-1 mol^-1.

Bah in my first post I wrote 0.0082 and not 0.0083.

My second post corrected this hence the 0.0083KJ/mol which is also equal to 8.314 J/K mol too. Just a little misunderstanding