A hydrogen-oxygen fuel cell stack delivers $1.00 kW$ of electrical power at a terminal voltage of $0.800 V$ for $1.00 h$ . Find the volume of oxygen consumed, in litres measured at STP (nearest integer). Take $F = 96500 C mo l^{- 1}$ , molar volume at STP $= 22.4 L$ .

Numerical answer type, answer in L, tolerance 2.

Answer: 261 L

Current

I = P / V = 1000/0.800 = 1250 A

; charge in one hour

Q = 1250 \times 3600 = 4.50 \times 1 0^{6} C

, i.e.

4.50 \times 1 0^{6} /96500 = 46.63 mol

of electrons. Cathode:

O X_{2} + 2 H X_{2} O + 4 e X^{-} 4 OH X^{-}

, so moles of

O X_{2} = 46.63/4 = 11.66 mol

. Volume at STP

= 11.66 \times 22.4 = 261 L