Question

(2) A fuel mixture used in the early days of rocketry is composed of two liquids, hydrazine (N2H4) and dinitrogen tetraoxide (N2O4), which ignite on contact to form nitrogen gas and water vapor.

Write the balanced equation for this reaction (include states of matter)

(3) If 1.50 × 102 g of N2H4 and 2.00 × 102 g of N2O4 are mixed, which is the limiting reactant?

(4) What is the theoretical yield (in grams) of N2 that can be produced when the quantities in part b) are mixed?

(5) If 155 g of N2 are actually obtained from the reaction, what is the percent yield?

Answer 1

Ans. #2. Balanced reaction: 2 N₂H₄(l) + N₂O₄(l) -------> 3 N₂(g) + 4 H₂O(g)

Theoretical molar ratio of reactants: N₂H₄ : N₂O₄ = 2 : 1

#3. Moles of N₂H₄ = Mass /Molar mass = 150 g / (32.04524 g/ mol) = 4.6809 mol

Moles of N₂O₄ = Mass /Molar mass = 200 g / (92.01108 g/ mol) = 2.1737 mol

Theoretical molar ratio of reactants: N₂H₄ : N₂O₄ = 4.6809 mol / 2.1737 mol = 2.15 : 1

# Comparing the theoretical and experimental molar ratios of reactants, the moles of N₂H₄ is greater than its theoretical value of 2 moles whereas that of N₂O₄ is kept constant at 1 mol.

Therefore, N₂H₄ is reagent in excess, and N₂O₄ is the limiting reactant.

#4. The formation of product follows the stoichiometry of limiting reactant.

According to the stoichiometry of balanced reaction, 1 mol N₂O₄ forms 3 mol N₂ gas.

So,

            Theoretical moles of N₂ formed = 3 x Moles of N₂O₄ consumed

                                                                        = 3 x 2.1737 mol

                                                                        = 6.5211 mol

            Theoretical mass of N₂ formed = Theoretical moles x Molar mass

                                                            = 6.5211 mol x (28.01348 g/ mol)

                                                            = 182.678 g

So, theoretical yield of N₂ = 182.679 g

#5. % yield of N₂ = (Actual yield / Theoretical yield) x 100

                                    = (155 g / 182.679 g) x 100

                                    = 84.85 %