Page 1 of 1

Intensive Property of Standard Cell Potential

Posted: Thu Feb 08, 2018 5:01 pm
by andrewr2H
In the example with the redox reaction between Fe3+(aq) and Cu(s) that Dr. Lavelle gave during Wednesday's lecture, he stated that because of the fact that standard cell potential is an intensive property, we do not double the value of Eo for the Fe3+ half reaction despite the fact that twice the amount of moles of Fe3+ were present in the reaction.

Redox Rxn:
2Fe3+(aq) + Cu(s) --> Cu2+(aq) + 2Fe2+(aq) Ecell= 0.43V

Half Rxns:
Fe3+ + 2e- --> Fe2+ Eo= 0.77V
Cu --> Cu2+ + 2e- Eo= -0.34V

I understand that an intensive property is a property that does not depend on the size of the sample or system, but I'm confused because when we were dealing with specific heat capacity (also an intensive property), the heat required to raise the temperature of a substance was dependent on the amount of that substance (q=m*Csp*dT). So as can be seen by this equation, the amount of heat is clearly dependent on mass. Why is this not the case when calculating cell potential?

Re: Intensive Property of Standard Cell Potential

Posted: Thu Feb 08, 2018 9:29 pm
by Lucian1F
The value of the specific heat itself is intrinsic because it will always be the same for some molecule at some phase. The specific heat does not change as mass does, the heat/energy does

Re: Intensive Property of Standard Cell Potential

Posted: Thu Feb 08, 2018 9:37 pm
by AnuPanneerselvam1H
Specific heat capacity is an extensive value and depends on the amount of substance present. Standard cell potential is an intensive value and does not depend on the amount of substance present.

Re: Intensive Property of Standard Cell Potential

Posted: Fri Feb 09, 2018 12:04 am
by Anna Okabe
The heat capacity is the one that is extensive, and specific heat capacity is actually intensive.
By "cell potential" are you referring to the standard reduction potential (Eo)? Because if so, the reason why you wouldn't change the Eo is because that is the voltage difference between the two standard electrodes. This voltage difference is constant, so that is why it doesn't depend on the number of time/miles you are using.