74grams of H2 gas and an excess of O2 gas reacts to form H2O according to the reaction below. What mass of H2O is produced? 2 H2(g) + O2(g) > 2 H2O(g)

Question

74grams of H2 gas and an excess of O2 gas reacts to form H2O according to the reaction below. What mass of H2O is produced? 2 H2(g) + O2(g) > 2 H2O(g)

Answer 1

First, the periodic table tells us that the mass of H is 1.008g, so H2 is 2.016g. 1 mol H2 is equal to 2.016g H2, so begin with 74g H2 and multiply it by 1 mol H2/2g H2 to convert to mols:

74g H2 X 1 mol H2/2g H2 = 37 mols H2.

 

We need to convert mols H2 to mols H2O, so we look at the balanced equation. They both have 2 mols, so we multiply 37 mols H2 by 2 mols H2O/2 mols H2:

37 mols H2 X 2 mols H2O/2 mols H2 = 37 mols H2O.

 

Now, we have to convert mols H2O to grams to find out "what mass of H2O is produced". The periodic table tells us that H2 is 2.016g and O is 16g, so 18g H2O is equal to 1 mol H2O.

37 mols H2O X 18g H2O/1 mol H2O = 666g H2O

 

74g H2 X 1 mol H2/2g H2 X 2 mols H2O/2 mols H2 X 18g H2O/1 mol H2O = 666g H2O