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Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: Joniaguis on May 02, 2009, 05:28:43 PM

Title: Entropy calculation
Post by: Joniaguis on May 02, 2009, 05:28:43 PM

I need some assistance over the following question. I don't know exactly which equation I have to use.

Determine the entropy change when one mole of a liquid (bpt 356K) is heated from 298K up to 428K given the following information:

Cp of liquid: 45 cal/mole/degree
Cp of vapour: 10.8 + 3.35 x 10^-2 T + 0.95 x 10^-4 T² cal/mole/degree
heat of vapourisation: 4405 cal/mole

Title: Re: Entropy calculation
Post by: o0CY0o on May 03, 2009, 01:51:29 AM

Quote from: Joniaguis on May 02, 2009, 05:28:43 PM

I need some assistance over the following question. I don't know exactly which equation I have to use.

Determine the entropy change when one mole of a liquid (bpt 356K) is heated from 298K up to 428K given the following information:

Cp of liquid: 45 cal/mole/degree
Cp of vapour: 10.8 + 3.35 x 10^-2 T + 0.95 x 10^-4 T² cal/mole/degree
heat of vapourisation: 4405 cal/mole

For this question, we need to consider 3 steps.
one the entropy change for liquid form 298K to 356K. 2nd the entropy for phase change. 3rd entropy change of gas phase from 356K to 428K


1.  :delta:S= 45 ln (356/298)
2.  :delta:S= :delta:H/T  = 4405/356
3.   :delta:S= intergrate C/T with respect to T for upper limit is 428 and lower limit is 356 where C is taken as 10.8 + 3.35 x 10^-2 T + 0.95 x 10^-4 T² cal/mole/degree.