Question

5 – If a hydrogen fuel cell runs an electric motor drawing a current of 8.5 A for 3.0 h, what volume of H2(g) is needed if the fuel is stored at 155 atm and 25 °C? (Ideal gas law required. Assume H2 behaves as an ideal gas under these conditions.)

6 – Chromium plating can be applied by electrolysis to objects according to the following unbalanced half-reaction: Cr2O72- + e- + H+ → Cr(s) + H2O

Answer 1

5) Current, c = 8.5 A = 8.5 (:-1A=19) Time, t = 3.0 h 3600s 1h = 10800 S Charge transferred, q = cxt =(85)< (10300 s) = 91800 C Thus, the charge transferred in the cell is 91800 C - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Cathode half-reaction: 4H2O(1)+ 4e —2H2(g) +40H" (aq) Charge carried by 1 mole of electrons = 96500 C 4 mole of electrons transferred in the cell to deposit 2 mol H, Charge transferred in the cell = 91800 C Amount of H, deposited by 378 C of charge = 91800 Cx 1 mol e 2 mol H, = 91800 CX 96500 C 4 mole = 0.476 mol H2 Pressure of the gas, P =155 atm Temperature, T = 298 K Gas constant, R= 0.0821 L.atm K-mol-1 According to ideal gas equation, PV = nRT Volume of the gas, V = ** (0.476 mol)(0.0821 L. (286) 155 atm = 0.0751 L = 75.1 mL