How many grams of H2O

Question

How many grams of H2O will be produced by the reaction of 17g of hydrogen gas and 75g of oxygen gas? [HINT: You must write a balanced chemical equation to do this problem.]

Answer 1

First write the balanced equation.

 

2H₂ + O₂ → 2H₂O

 

Now figure out how many moles of each reactant there are, and how many moles of product can be made from them.

 

17g H₂ x 1 mol H₂/2.01588g H₂ x 2 mol H₂O/2 mol H₂ = 8.43304 mol H₂O

75g O₂ x 1 mol O₂/31.9988g O₂ x 2 mol H₂O/1 mol O₂ = 4.68768 mol H₂O

 

So upon making 4.68768 moles of H₂O the O₂ will be depleted and no more H₂O will be made, even though not all of the H₂ was used.  Now convert to grams.

 

4.68768 mol H₂O x 18.01528g H₂O/1 mol H₂O = 84.44987g H₂O

 

Using significant figures, 84g of H₂O will be produced.