Question

(a)For the reaction :
`2AgCl (s) + H_(2)(g) ` (1 atm) ` to 2 Ag(s) + 2H^(+) (0.1M) + 2Cl^(-) (0.1M) , DeltaG^(@) = -43600J` at `25^(@)`C.
Calculate the e.m.f. of the cell . [log `10^(-n) = -n`].
(b) Define fuel cell and write its two advantages.

Answer 1

(a) `2AgCl(s) + H_(2)(g)` (1 atm) `to 2Ag(s) + 2H^(+) (0.1M) + 2Cl^(-) (0.1M)`
`DeltaG^(@) = -43600 J` at `25^(@)C`
`Delta G^(@) = - n F E^(@)` cell `" "` [n =2]
`-43600 = -2 xx 96500 E^(@)` cell
`E_("cell")^(@) = (cancel43600^(218))/(cancel2 xx cancel 96500)`
`E_("cell")^(@) = 0.225V`
`E_("cell")^(@) = E_("cell")^(@) - (0.0591)/(2) "log"([H^(+)]^(2)[Cl^(-)]^(2))/(1) = 0.025 - (0.0591)/(2) "log" 0.1 xx 0.1 xx 0.1 xx 0.1`
`= 0.225 - 0.02955 "log" 10^(-4) = 0.225 - 0.02955 xx (-4) = 0.225 + 0.1182`
`E_("cell")^(@) = 0.3432V`
(b) Fuel cell : A device in which the heat produced as a result of the combustion of fuel (like `H_(2) - O_(2)`) is converted into electricity is called fuel cells.
Advantages : (i) Because of the continous supply , fuel cell never become dead .
(ii) They do not cause any pollution problem unlike thermal plants which burn fossils fuels like coal , gas oil etc.
(iii) They give an efficiency of 60-70% which is superior to thermal plants.