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Mole Relations in Balanced Equations

Worked Problem: Mole Relations in Balanced Equations

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Chemical equations state moles of reactants and products.

Chemical equations state moles of reactants and products.

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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

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