Question

Given the balanced equation representing a reaction:2H2 + O2 ==> 2H2O

What is the mass of H2O produced when 10.0 grams of H2 react completely with 80.0 grams of O2?
(1) 70.0 g (2) 90.0 g (3) 180. g (4) 800. g

Answer 1

The answer is (2) 90.0 g. The reaction equation represents the ratio of mole number of every compounds. So we need to transfer the mass to mol first. There is 5 mol H2 and 5 mol O2. According to equation, we can know production is 5 mol, too. So the mass is 90 g.