Calculate the mass of water produced when 25.0g of oxygen gas react with 42.0g of hydrogen gas.
2H2 + O2 -> 2H,0

Reaction.-

2H2 + O2 ---> 2H2O

Given,

Mass of Oxygen - 25.0 g

Mass of Hydrogen - 42.0 g

now we have to calculate moles

moles of O2 = 25/16 = 1.5625 moles

Moles of H2 = 42/2 = 21 moles

Hydrogen gas is in excess,

now using reaction

1 mole of oxygen gas forms 2 moles of H2O

1.5625 mole of Oxygen gas will form x mole of H20

x = 3.125 moles

molar mass of H2O is 18g

mass of 3.125moles of water = 3.125 × 18 = 56.25 g.

Hence the mass of water produced when 25.0g of oxygen gas react with 42.0g of hydrogen gas is 56.25 grams