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Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: HelloCthulhu on December 15, 2014, 01:50:32 PM

Title: Electrolysis System Work for 1ml of Water
Post by: HelloCthulhu on December 15, 2014, 01:50:32 PM
I'm trying to convert the standard system work for the electrolysis of water for 1ml.

From http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/electrol.html

W = PΔV = (101.3 x 103 Pa)(1.5 moles)(-22.4 x 10-3 m3/mol)(298K/273K) = -3715

I know that I must convert moles to millimoles, but I still don't understand how to adjust for Ideal Gas Law. Any help is greatly appreciated!
Title: Re: Electrolysis System Work for 1ml of Water
Post by: mjc123 on December 16, 2014, 05:14:06 AM
What do you mean by "adjust for the ideal gas law"? It's a simple matter of proportionality. You have the work for the electrolysis of 1 mole of water. You want the work for the electrolysis of 1 ml. How many moles in 1 ml of water?
Title: Re: Electrolysis System Work for 1ml of Water
Post by: HelloCthulhu on December 16, 2014, 02:43:26 PM
Thanks for the response! I think I found what I was looking for though.

http://en.wikipedia.org/wiki/Van_der_Waals_equation
Title: Re: Electrolysis System Work for 1ml of Water
Post by: mjc123 on December 17, 2014, 05:17:58 AM
Why do you need vdW equation? Were you asking a totally different question from what you appeared to be?
Title: Re: Electrolysis System Work for 1ml of Water
Post by: HelloCthulhu on December 17, 2014, 10:32:40 AM
Since I'm not working under standard conditions, I shouldn't be using Idea Gas Law. To adjust for real gas, I have to use the VDW equation. This video really clarified the difference for me:

https://www.youtube.com/watch?v=GIPrsWuSkQc
Title: Re: Electrolysis System Work for 1ml of Water
Post by: Borek on December 17, 2014, 12:07:39 PM
Since I'm not working under standard conditions, I shouldn't be using Idea Gas Law.

Accuracy of ideal gas law is not a matter of using it at standard conditions. Depending on the accuracy required you may already need corrections at STP.

Quote
To adjust for real gas, I have to use the VDW equation.

Yes and no. Whether you need a better formula than the ideal gas equation depends on the accuracy required and the conditions. Yes, sometimes VdW equation will give better results, but sometimes using it is just making life harder without any benefits.