Question

2 C2H6 + 702 — 4 CO2 + 6H2O

Answer 1

We calculate the number of moles of water given its mass by dividing the mass by the molar mass.  

                              n water = (36.04 g) / (18 g/mol)  

                               n water = 2 mols

From the given balanced equation, every 6 moles of water produced will require 7 moles of oxygen.

                               n oxygen = (2 mols H2O) x (7 moles O2 / 6 moles H2O)

                               n oxygen  = 2.33 mols O2