# What pressure units should be used when calculating electrode potential with Nernst equation?

Example 17: Calculate the electrode potential of given electrode $$\ce{Pt,Cl2 (\pu{1.5 bar}) | 2 Cl- (\pu{0.01 M})}\,; \quad E^\circ_\ce{Cl2/2Cl-} = \pu{1.36 V}$$

Solution: The reaction of electrode is $$\ce{\underset{\pu{1.5 bar}}{Cl2 (g)} + 2 e- -> \underset{\pu{0.01 M}}{2 Cl-}}$$ $$E = E^\circ - \frac{0.0591}{n}\log{\frac{[\ce{Cl-}]^2}{P_\ce{Cl2}}} = 1.36 - \frac{0.0591}{2}\log{\frac{(0.01)^2}{1.5}} = \pu{1.483 V}$$

In the solution, the author has directly used the pressure (which is in bars) in the Nernst equation without first converting it to its SI units. How can this be right?

• I would recommend to properly rotate the image, or, even better, type the stuff using MathJax. Most people won't bother trying to decipher what's been photocopied and will just down-vote. Also, Nernst is a name of scientist and should be capitalized, whereas bar is a unit and shouldn't be capitalized. – andselisk Jan 3 '18 at 11:19
• @andselisk Sure, I'll keep that in mind. – Senthil Arihant Jan 3 '18 at 12:04
• I edited the question for you, feel free to check out whether it's correct; also you can visit this page, this page and this one on how to format your future posts better with MathJax and Markdown. – andselisk Jan 3 '18 at 12:06
• No prob at all, just spare some free time and get to know these formatting features; otherwise, as I said, questions are often getting closed and downvoted because of that. – andselisk Jan 3 '18 at 12:09

Fugacity is defined with a reference to the standard state with the pressure of $\pu{10^5 Pa}$ or $\pu{1 bar}$. At ordinary pressures fugacity is numerically approximately equal to the pressure expressed in bars or atmospheres ($\pu{1 bar} \approx \pu{0.987 atm}$), so the author of the book is right.