I only need help with question 7.65, this is a Physical Chemistry question from

Question

I only need help with question 7.65, this is a Physical Chemistry question from Physical Chemistry (Silbey, Bawerti, Abendi) (4th edition)

The Calomel electrode is: Cl-(aq) l Hg2Cl2 (s) l Hg (l)

I know that the answer is: (a) 2.62 (b) 2.399 x 10-3

I just need help working the problem and setting it up.

7.64 A hydrogen-oxygen fuel cell is operated at 25°C and a total pressure of 5 bar. What is the electromotive force, assuming the gases are ideal? 7.65 A hydrogen electrode and a normal calomel electrode give an electromotive force of 0.435 V when placed in a certain solution at 25°C. (a) What is the pH of the solution? (b) What is the value of aH? 7.66 A mole of H2O1) is electrolyzed at 298 K and 1 bar. (a) How much electrical energy is required if there are no losses due to electrical resistance and overvoltage? (b) The hydrogern and oxygen are then burned at constant pressure to produce one mole of H2O() at 298 K and 1 bar. How much heat is produced? (c Can this heat be used in a heat engine to produce the amount

Explanation / Answer

a)

The EMF of the cell is given by

Ecell = (Eocalomel- Eo H+/Pt) + (0.05913V) pH

Eocalomel = 0.280 (literature value)

Eo H+/Pt = 0.0 V (SHE)

Ecell =0.435 V (Given data)

Substituting the values in the above equation

0.435 = (0.280 - 0.0) + 0.05913 pH

so pH = (0.435 - 0.280) / 0.05913 = 0.155/ 0.05913 = 2.62

So the pH of the solution is 2.62

b)

pH =-log [aH+]

2.62 = -log [aH+]

aH+ = 10(-2.62)

aH+ =2.398x10-3

So the value of aH+ is 2.398x10-3

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