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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: barnyard on January 25, 2007, 12:56:03 AM

Title: Clausius-Clapeyron Equation - having probs w/ a question
Post by: barnyard on January 25, 2007, 12:56:03 AM
whats up guys, ive been having problems on this h/w problem using the clausius-clapeyron equation to find the pressure of a gas.. ive gotten some of the other same types of questions correct but i keep getting the same answer and its wrong..

Diethyl ether has a DELTA H vap of 29.1 kJ/mol and a vapor pressure of .703 atm at 25 degrees Celsius.  What is its vapor pressure at 55 degrees celcius..

ln P2/P1 = ( - H vap/R)(1/T2-1/T1)

             = (-29100/8.314)(1/323.15 - 1/298.15)

i always get it to come out to lnP2/P1 = .908
so my final answer keeps coming to 1.74  which is off by 10%-100%

when i initially submitted the problems answer as 1.88 atm it said i was within 10 percent..


i didn't think i had a calculation error b/c ive done it like 5 times using all different ways (using torr instead of atm, converting scientific notation to very small decimal numbers, etc...)  i always get to the last step where i have .908 = lnP2/P1

any ideas i should try???
thanks a whole lot



Title: Re: Clausius-Clapeyron Equation - having probs w/ a question
Post by: Yggdrasil on January 25, 2007, 02:38:37 PM
You have the right idea but the wrong numbers.

55o = 328 K not 323 K

It's amazing the differene that 5K can make.