For spontaneity it can either be spontaneous or non-spontaneous Delta degree and

Question

For spontaneity it can either be spontaneous or non-spontaneous

Delta degree and E degree can be said to measure the same thing, and are convertible by the equation Delta G degree = -nFE^degree_cell where n is the total number of moles of electrons being transferred, and F is the Faraday constant 9.64853415 times 10^4 C/mol. The free energy (Delta G degree) of a spontaneous reaction is always negative. For each of the electrochemical cells below, calculate the free energy of the system and state whether the reaction is spontaneous or non-spontaneous as written based on the cathode and anode assignment given. (Use the table of Standard Electrode Potentials.) The cathode is Au(III) and the anode is Ag(I). The cathode is Cd(II) and the anode is Sn(II). The cathode is Mn(II) and the anode is Al.

Explanation / Answer

a)

for

Au and Ag

Au3+ + 3 e Au(s) +1.52

Ag+ + e Ag(s) +0.7996

E°cell = Ecathode - Eanode = 1.52-0.7996 = 0.7204

dG = nF*E°cell = -3*96500*0.7204 = -208555.8 J = 208.55 kJ

this favours forward

b)

Cd2+ + 2 e Cd(s) 0.40

n2+ + 2 e Sn(s) 0.13

E°cell = -40 - (-0.13) = -0.27 V

G = -nF*E°Cell = (2)(96500)(0.27) = 52110 J = 52.11 kJ

this does NOT favours forward raction

c)

Mn+2 to Al

Mn2+ + 2 e Mn(s) 1.185

Al3+ + 3 e Al(s) 1.662

E°cell = -1.185 - -1.662 = 0.477V

dG = -nF*E°cell = -6*96500*0.477 = 276183 J = -276.183 kJ

this favours forward direction

Related Questions

Navigate

• Browse (All)
• Browse F
• Subjects

---