Question

III O ELECTROCHEMISTRY Recognizing consistency among equilibrium constant, free... A student made measurements on some electrochemical cells and calculated three quantities: . The standard reaction free energy Agº. . The equilibrium constant Kat 25.0*c. • The cell potential under standard conditions E. His results are listed below. Unfortunately, the student may have made some mistakes. Examine his results carefully and tick the box next to the incorrect quantity in each row, if any. Note: If there is a mistake in a row, only one of the three quantities listed is wrong. Also, you may assume the number of significant digits in each quantity is correct. Also note: for each cell, the number n of electrons transferred per redox reaction is 1. calculated quantities (Check the box next to any that are wrong.) cell 40 А 123. J/mol O -22 2.83 x 10 o 1.27 V B -142 kJ/molo 1.33 x 10 1.47 V o С 20. /molo 3.19 x 10 x 10² o -0.21 V х ? Explanation Check

Answer 1

  = - nFE^o

AGO

and , = - RTlnK.

AGO

So, when , is negative , E^o is positive and K > 1

AGO

When, is positive, E^o negative and K < 1.

AGO

A.

Given , is positive , and K < 1 so E^o must be negative , but Value of E^o = 1.27 V.

AGO

Hence, in row A, E^o value is wrong.

B.

Given, is negative (-152 KJ/mol).

AGO

So, E^o must be positive, given value of E^o is positive and K > 1.

But value of K = 1.33× 10^-25 which means < 1, which is not possible.

Therefore in row B, wrong is K.

C.

Given , is positive ,

AGO

So E^o must be negative and K < 1.

Given Value of E^o = - 0.21

and , K = 3.19 × 10³ which means K >1 , which is not possible.

Therefore in row C,. wrong is K.