Q. 26

# Calculate emf <sp

We know that,

cell = E˚C - E˚A

Ecell = 0.80 – (-2.37)

Ecell = 3.17 V

Anode reaction: Mg Mg2+ + 2e-

Cathode reaction: 2Ag+ + 2e- 2Ag (By multiplying by 2 to equate the number of electrons)

Cell reaction: Mg + 2Ag+ Mg2+ + 2Ag

According to Nernst Equation,

Ecell = E˚cell log [Mg2+]/[Ag+]2

= 3.17 – log [0.1]/ [0.0001]2

= 3.17 – 0.0295 log [0.1]/ [1x 10-8]

= 3.17 – 0.0295[ log0.1 + log108]

= 3.17 – 0.0295[-1 + 8]

= 3.17 – 0.0295(7) = 3.17 – 0.2065

Ecell = 2.9635 V G = -nfE˚cell

= -2 x 96500 x 3.17 G = -611.810 kJ/mol

OR

(a) We know that,

C = 0.001 mol/L and k = 4.95 x 10-5 S/cm

Molar conductivity = = 4.95 10-5 x = 49.5 S cm2/mol

CH3COOH = CH3COO- + H+ (CH3COOH)= (CH3COO-) + (H+)

= 40.9 + 349.6

= 390.5 S cm2/mol

Degree of dissociation = m / m

= Degree of dissociation = 0.12

(b)

• A fuel cell is defined as a class of devices that converts chemical energy directly into electricity by chemical reactions.

• An example is a H2O2 fuel cell which was also used to produce energy during the Apollo Space Program.

• Fuel cells have higher efficiency than ordinary cells. They also do not produce a lot of pollution.

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