Sign for Standard Reduction Potentials


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Katie Clark 3B
Posts: 26
Joined: Fri Sep 25, 2015 3:00 am

Sign for Standard Reduction Potentials

Postby Katie Clark 3B » Fri Feb 19, 2016 4:41 pm

I'm wondering when the sign of standard E changes. On question 8 on the midterm, the oxidation half reaction was Cd->Cd2+ + 2e-. In the formula sheets we are given, the standard E=-0.40 V for Cd2++2e-->Cd. However, in the answer key, the standard E for the half reaction is 0.40 V. Why is this?

tianying_feng_3J
Posts: 21
Joined: Fri Sep 25, 2015 3:00 am

Re: Sign for Standard Reduction Potentials

Postby tianying_feng_3J » Fri Feb 19, 2016 5:47 pm

the +0.40V is the E for oxidation
basically the answer skips the step(s) where you first find the half reduction equation for Cd2++2e-->Cd and the corresponding E(red)=-0.40V, then you flip the equation to get the oxidation equation and the E(oxi)=+0.40V


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