February 16th, 2017, 12:39 AM  #1 
Newbie Joined: Feb 2017 From: Lebanon Posts: 18 Thanks: 1  Entropy Calculation
Can any one please help me to solve this? Calculate the entropy change if one mole of water evaporate at 373 K and 1 atm. If you look up the enthalpy of vaporization, for water in a table, you would get a molar enthalpy of 40.7 kJ/mol. 
February 17th, 2017, 06:05 AM  #2 
Senior Member Joined: Apr 2014 From: Glasgow Posts: 2,037 Thanks: 674 Math Focus: Physics, mathematical modelling, numerical and computational solutions 
For the case of constant temperature: Change in entropy = Change in heat content / T $\displaystyle \Delta S = \frac{\Delta Q}{T}$ For latent heat transfer (evaporation): $\displaystyle \Delta Q = \Delta m \times l$ = 1 mole x latent energy per mole = 40700 J $\displaystyle \Delta S = \frac{\Delta Q}{T} = \frac{40700}{373} = 109.12 $ J/K 
February 20th, 2017, 09:15 PM  #3  
Newbie Joined: Feb 2017 From: Lebanon Posts: 18 Thanks: 1  Entropy Calculation Quote:
Well I have another entropy related question, I was searching for material for more information about entropy conversions. I come to know about MMPBSA Charmm, I read out some information and have some query related entropy conversion. My question is: What is the conversion that charmm uses for convert the entropic units to kcal/mol? In the scripts I found the MMPBSA script and I see that to obtain the entropy in kcal/mol only multiply by temperature, is that correct? That may implicated the 1 eu = 1kcal/mol. Last edited by JamSmith; February 20th, 2017 at 09:24 PM.  
February 21st, 2017, 01:24 AM  #4 
Senior Member Joined: Apr 2014 From: Glasgow Posts: 2,037 Thanks: 674 Math Focus: Physics, mathematical modelling, numerical and computational solutions 
I have no idea what CHARMM is, so I can'#t really answer your question, but the response to (presumably) your post here: https://www.charmm.org/ubbthreads/ub...at&Number=5712 seems correct. It's just the formula in my post; you're basically calculating heat from entropy. 

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calculation, entropy, entropy conversion 
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