Question

In the explosion of a hydrogen-filled balloon, 0.50g of hydrogen reacts with 4.0g of oxygen to form water vapor. How much water vapor is formed?

Answer 1

first write the balanced equation

2 H2 + O2 ---> 2 H2O

0.50 g H2 x (1 mole / 2g) = 0.25 moles H2

4.00 g O2 x (1 mole / 32g) = 0.125 moles O2

from balanced equation, 2 moles H2 react with 1 mole O2.. therefore

0.25 moles H2 x (1 mole O2 / 2 moles H2) = 0.125 moles O2

since we need 0.125 moles O2 to react with all the H2 and we have exactly that amount, the amounts are said to be

"stoichiometric" and either reactant can be considered limiting

from the balanced equation, 2 moles H2 --> 2 moles H2O.. therefore

0.25 moles H2 x (2 moles H2O / 2 moles H2) = 0.25 moles H2O

finally..

0.25 moles H2O x (18.0 g / mole) = 4.5 g H2O