How many water molecules (h2o) can be produced from 6 molecules of hydrogen gas (purple) reacting with 6 molecules of oxygen gas (turquoise)? which reactant is the limiting reactant?

oxygen and hydrogen molecules
a. 6 water molecules, hydrogen is limiting
b. 3 water molecules, oxygen is limiting
c. 3 water molecules, hydrogen is limiting
d. 12 water molecules, oxygen is limiting

Hydrogen gas reacts with oxygen gas to form water according to the equation


From the coefficients in the reaction equation, we can see that it takes two molecules of hydrogen to react with one molecule of oxygen. Since we begin with equal amounts of both gasses, we can conclude that hydrogen is the limiting reactant because we use it up first. Thus, we use hydrogen for our stoichiometry that follows.


Thus, the answer is B, 6 water molecules are produced with hydrogen being the limiting reactant

the catch is that the top numbers are atomic masses the bottom numbers are the numbers of protons and electrons in an uncharged atom. they are the number of that atoms as you would find them on the periodic table. further, the numbers on the left are used to determine the missing numbers on the right

so here we go

atomic mass

239 + 1 = y + 134 + 3 combine like terms

240 = y + 137             subtract 137 from both terms

240 - 137 = y

103 = y

atomic number

94 = z +54 + 0

94 = z + 54               subtract 54 from both sides.

40 = z

answer