Q. 26

Calculate emf <sp

Answer :


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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