# Do We change sign of electrode potential when reversing an equation?

I have a cell equation as:

$$\ce{2Cr^0 + 3Cd^2+ -> 2Cr^3+ + 3Cd^0}$$

I am provided the standard reduction potentials as:

\begin{align}\ce{Cd^2+ + 2e- &-> Cd} && E= \pu{-0.4V}\\ \ce{Cr^3+ + 3e- &-> Cr} && E= \pu{-0.74V}\end{align}

Now do I use chromium’s reduction potential as $$\pu{-0.74V}$$ or do I flip the equation and use $$\pu{+0.74V}$$ (as it is getting oxidised and I have the equation for reduction)?

This is using the formula $$E(\text{cell}) = E(\text{cathode}) -E(\text{anode})$$, all reduction potentials.

• $$\ce{Cr^{3+} + 3e^- -> Cr}\quad\quad\quad\text{E = -0.74}$$ $$\ce{Cr -> Cr^{3+} + 3e^- }\quad\quad\quad\text{E = +0.74}$$ – MaxW Dec 16 '18 at 8:59
• A few notes: I (the pronoun) is capitalised in English, colons are typeset directly attached to the preceeding words (no space), dashes after colons are discouraged, physical values need a unit and there is a space before the opening bracket. – Jan Dec 16 '18 at 16:03

The reduction potentials are a special case of standard reaction enthalpy, because you can transform $$\Delta E$$ into $$\Delta H$$ just by calculating with a few constants.