Now, to take a tottering step forward, dropping all pretence at accuracy, Avogadro's constant is about 10^24, so you are going to run into 10^-11 grams of oxygen per second, to fuel your jet, which'll combine with 10^-12 g of H. So you'll develop a power of about 10^-7 W at 100% efficiency.
I'll leave it to someone else to work out how much power it'll take to push through the excess hydrogen.
Cheers
Greg Locock