Difference between equations for calculating Ecell


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Aoife Galvin 2D
Posts: 9
Joined: Fri Sep 25, 2015 3:00 am

Difference between equations for calculating Ecell

Postby Aoife Galvin 2D » Sun Feb 28, 2016 11:34 pm

There are two formulas in the course reader for calculating E:
E = E standard - ((RT)/(nF))(lnQ)
E = E standard - (0.0592/n)(logQ)
And I was wondering what the difference between the two was, i.e. what are the circumstances when you use each one and why are there two different equations for the same thing?

Natasha Szombathy 3I
Posts: 12
Joined: Fri Sep 25, 2015 3:00 am

Re: Difference between equations for calculating Ecell

Postby Natasha Szombathy 3I » Sun Feb 28, 2016 11:39 pm

You can use both equations interchangeably, as long as your reaction is occurring at 298K.

Ashlee Joan Macalino 3J
Posts: 36
Joined: Fri Sep 25, 2015 3:00 am

Re: Difference between equations for calculating Ecell

Postby Ashlee Joan Macalino 3J » Sun Feb 28, 2016 11:40 pm

There isn't a difference between the two equations. The second equation is a simplified or expedited version that divides the gas constant, R, by Faraday's constant, F. You can use whichever one is easiest and most convenient for you. Just remember that one equation is in terms of log base 10 and the other is in terms of the natural logarithm, ln.

Peiliang Zhou 3K
Posts: 21
Joined: Fri Sep 25, 2015 3:00 am

Re: Difference between equations for calculating Ecell

Postby Peiliang Zhou 3K » Sun Feb 28, 2016 11:46 pm

E = E standard - (0.0592/n)(logQ) is the equation used when you know the system is under standard conditions. It is essentially the same as E = E standard - ((RT)/(nF))(lnQ) except T will be constant at 25oC, and thus the calculation RT/F is a constant itself and is already done for you, and all there is left is n. Also, the equation can be E = E standard - (0.02569/n)(lnQ) if you want to use lnQ instead of logQ.

Hope this helps! :D


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