I50 ATOMS, IONS, SALTS, AND SURFACES 



Pi 

 In the special case given above, pi = io and p2 = i, and log t^=i, the number of 



P^ 



mols of hydrogen (N) transferred is \ and the number of charges transferred (91) is 

 I, so 



96,500 



If the temperature is 25° C, then r= 270+ 25 = 298° K., and (g = °-°59i5 volts = 



0.02957 volts. 



A cell may contain two aqueous solutions with diliferent hydrogen-ion concen- 

 trations, such as 



M+H2 {p atm.), H+Cl- {nh molal), H+Cl- (w. molal), M+fl^, {p atm.) . 



Now if I Faraday of positive electricity is passed from left to right, the following 

 changes occur: 



Left Electrode 



IT 



— ip atm.) -^ H+ (;«, molal) , 

 2 



Liquid Junction 



T^jj + )H+ (nil molal) -^ ^(/7 + ) ^'^ (^2 molal) , 

 T(^Qi^^Cl~ [niz molal) -^ T^ (Ci-) CZ+Cmi molal) , 



Right Electrode 



U+ (w. molal) — [p atm.) . 

 2 



If the changes at the electrode are alone considered it is found that as much hy- 

 drogen {H2/2) appears at p atm. as disappears at that pressure, so this change involves 

 no work, and therefore no electromotive force. 



If the liquid junction is neglected for the moment, the total remaining change is 



H+{tn2 molal) -> H+ (nii molal) 

 and 



@£ = -sT?r- ^« — (Approximate) , 

 or 



^E = -^^r^ In - (Exact) . 



Here iV/9^ = i. For the liquid junction potential, 



K r,. , RT , Wi I ^ RT , Ml 



g nii iS nh 



rj. , RT m2 . rj. RT , W2 



= -T{H+) -^ In \-T(Ci-) -^ In ~ , 



