H2 and o2 react to produce h2o. what is the mass of h2o produced when 0.73 g of h2 completely reacts with 3.28 g of o2 ?

Hydrogen reacts with oxygen based on the following equation:
2 H2 + O2 → 2 H2O

From the periodic table:
molar mass of hydrogen = 1 gram
molar mass of oxygen = 16 grams

From the balanced equation above, we can find that:
4 grams of hydrogen react with 32 grams of oxygen to produce 36 grams of water.

This means that: 0.73 grams of hydrogen require (0.73x32) / 4 = 5.84 grams of oxygen to react with.
Since only 3.28 grams of oxygen are reacting, this means that oxygen is our limiting reagent and that the reaction would stop once the amount of oxygen is consumed.

So, we will base our calculations on oxygen.
mass of water produced from 3.28 grams of oxygen can be calculated as follows:
mass of water = (3.28 x 36) / 32 = 3.69 grams

It changes food into energy that the organism can use.