Balance your chemical reaction first. Start by balancing carbon so you have 2 carbons on both sides.
C2H6 + O2 —> 2CO2 + H2O
Now balance your hydrogen so you have 6 hydrogens on both sides.
C2H6 + O2 —> 2CO2 + 3H2O
Now balance your oxygens. You have 7 oxygens on the right and 2 on the left, so multiply O2 by 3.5.
C2H6 + 3.5O2 —> 2CO2 + 3H2O
However, you can’t have a decimal in a coefficient. So, multiply everything by two.
2C2H6 + 7O2 —> 4CO2 + 6H2O
Now use your mole ratio of 6 mol H2O for every 2 mol of C2H6 to solve.
1.4 mol C2H6 • 6 mol H2O / 2 mol C2H6 = 4.2 mol H2O
D) 4.2 moles
