The hydrogen-oxygen fuel cell is described in the text. For the questions below,

Question

The hydrogen-oxygen fuel cell is described in the text. For the questions below, assume the following: Assume that the air is 20% O_2 by volume and that all the O_2 is consumed in the cell. The other components of air do not affect the fuel-cell reactions. Assume ideal gas behavior. (a) What volume of H2(g), stored at 25.0 degree C at a pressure of 141 atm, would be needed to run an electric motor drawing a current of 8.50 A for 3.00 hr? L (b) What volume (in liters) of air at 25.0 degree C and 1.05 atm will have to pass into the cell per minute to run the motor? L/min

Explanation / Answer

Soloution:-
2H2(g) + O2(g) -----> 2H2O(l)
E°cell = 1.23 V
PART (A):-
current=8.5 AMP
Time =3h
T =298k
p=141atm
n=8.5 Amps × 3 hours ×(3600 sec/1 hour) × (1 C/1 Amp×sec) = 91800 C × (1 mol e-/96500 C) = 0.951 mol
e-0.951 mol e- × (2 mol H2/4 mol e-) = 0.476 mol H2
V = (nRT)/P
(nRT)/P= (0.476 mol H2×0.0821×298 K)/141 atm = 0.08259376L H2
v= 0.08259376L H2

For part (B):-
R=0.238mol o2
T=298k
p=1atm
n=0.951 mol e- × (1 mol O2/4 mol e-) = 0.238 mol O2
V = (nRT)/P
V=( 0.238mol O2 ×0.0821 × 298K)/1 atm =5.82 L

Assume that air is 20% O2 by volume
5.82 L /20% = 29.11 L

V1=29.11L

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