What is the mass of water produced when 5 moles of hydrogen burn in the presence of excess oxygen?

Answer 1

2H2 + O2 ==> 2H2O
2 mols H2 will produce 2 mols H2O; therefore, 5 mols H2 will produce 5 mols H2O.
g H2O = mols H2O x molar mass H2O.