Mole Relations in Balanced Equations

These are worked chemistry problems showing how to calculate the number of moles of reactants or products in a balanced chemical equation.

Mole Relations Problem #1

Determine the number of moles of N₂O₄ needed to react completely with 3.62 mol of N₂H₄ for the reaction 2 N₂H₄(l) + N₂O₄(l) --> 3 N₂(g) + 4 H₂O(l)

Solution

Find the relation between moles of N₂H₄ and N₂O₄ by using the coefficients of the balanced equation:

2 mol N₂H₄ is proportional to 1 mol N₂O₄

Therefore, the conversion factor is 1 mol N₂O₄/2 mol N₂H₄:

moles N₂O₄ = 3.62 mol N₂H₄ x 1 mol N₂O₄/2 mol N₂H₄

moles N₂O₄ = 1.81 mol N₂O₄

Answer

1.81 mol N₂O₄

Mole Relations Problem #2

Determine the number of moles of N₂ produced for the reaction 2 N₂H₄(l) + N₂O₄(l) --> 3 N₂(g) + 4 H₂O(l) when the reaction begins with 1.24 moles of N₂H₄.

Solution

Find the relation between moles of N₂H₄ and N₂ by using the coefficients of the balanced equation:

2 mol N₂H₄ is proportional to 3 mol N₂

In this case, we want to go from moles of N₂H₄ to moles of N₂, so the conversion factor is 3 mol N₂/2 mol N₂H₄:

moles N₂ = 1.24 mol N₂H₄ x 3 mol N₂/2 mol N₂H₄

moles N₂ = 1.86 mol N₂O₄

Answer

1.86 mol N₂