Question

Hydrazine (N2H4), a rocket fuel , reacts with oxygen to form nitrogen gas and water vapor. The reaction is represented with the equation:
N2H4(l) + O2(g) → N2(g) + 2H2O(g)

At STP, if 4.20L of O2 reacts with N2H4, how many liters of water vapor will be produced?

A)
2.10L H2O(g)


B)
2.67L H2O(g)


C)
5.33L H2O(g)


D)
8.40L H2O(g)

Answer 1

Answer:

D)  8.40 L H₂O(g).

Explanation:

• The balanced equation for the mentioned reaction is:

2N₂H₄(l) + O₂(g) → N₂(g) + 2H₂O(g),

It is clear that 2.0 moles of N₂H₄ react with 1.0 mole of O₂ to produce 2.0 moles of N₂ and 2.0 moles of H₂O.

• At STP, 4.20L of O₂ reacts with N₂H₄:

It is known that at STP: every 1.0 mol of any gas occupies 22.4 L.

using cross multiplication:

1.0 mol of O₂ represents → 22.4 L.

??? mol of O₂ represents → 4.2 L.

∴ 4.2 L of O₂ represents = (1.0 mol)(4.2 L)/(22.4 L) = 0.1875 mol.

• To find the no. of moles of H₂O produced:

Using cross multiplication:

1.0 mol of O₂ produce → 2.0 mol of H₂O, from stichiometry.

0.1875 mol of O₂ produce → ??? mol of H₂O.

∴ The no. of moles of H₂O = (2.0 mol)(0.1875 mol)/(1.0 mol) = 3.75 mol.

• Again, using cross multiplication:

1.0 mol of H₂O represents → 22.4 L, at STP.

3.75 mol of H₂O represents → ??? L.

∴ The no. of liters of water vapor will be produced = (3.75 mol)(22.4 L)/(1.0 mol) = 8.4 L.

So, the right choice is: D)  8.40 L H₂O(g).