Half Reactions: Balancing

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Michelle Velasco 1L
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Joined: Fri Sep 25, 2015 3:00 am

Half Reactions: Balancing

Postby Michelle Velasco 1L » Tue Feb 02, 2016 12:00 am

In the course reader (pg 50), there's an example concerning balancing half reactions and writing the cell res.

One of the original equations is:
Fe^ 3+ + -e -----> Fe^2+ E = 0.77 V

and when you balance it,
2Fe^3+ + 2 e- ----> 2Fe^2+ E=0.77 V

How come when the reaction is balance, the E value doesn't change even if the coefficients do?

Posts: 22
Joined: Fri Sep 25, 2015 3:00 am

Re: Half Reactions: Balancing

Postby LinaLi2E » Tue Feb 02, 2016 12:38 am

The standard reduction potential (E^o) is an intensive property, so that means that the size or amount of something in the system will not change its value. An example that Dr. Lavelle used in lecture was the density of water. At 20 degrees celsius, the density of water if 0.9982g/cm^3 whether you have 50mL or 50 L of water, the density remain the same. So whether you need 2 moles of Fe^3 or 1 Fe^3, the standard reduction potential will remain the same, 0.77v.

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