Question

Hydrazine (N₂H₄), a rocket fuel, reacts with oxygen to form nitrogen gas and water vapor. The reaction is represented with the equation:

N₂H₄(I) + 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?

Answer 1

At STP one mol weighs 22.4L

Moles of O_2

• 4.2/22.4
• 2.1/11.2
• 0.19mol

1 mol.O_2 can create 2mol water

moles of water

• 2(0.19)
• 0.38mol

Volume of water

• 0.38(22.4)
• 8.512L

Answer 2

The given equation is:

N2H4(l) + O2(g) → N2(g) + 2H2O(g)

From the periodic table:

• mass of nitrogen = 14 grams
• mass of hydrogen = 1 gram
• mass of oxygen = 16 grams

Therefore:

molar mass of N2H4 = 2(14) + 4(1) = 32 grams

mass of water = 2(1) + 16 = 18 grams

From the balanced equation:

1 moles of N2H4 produces 2 moles of H2O.

32 grams of N2H4 produce 18*2=36 grams of water

To know the mass of N2H4 needed to produce 96 grams of water, all you need to do is cross multiplication as follows:

mass of N2H4 = (96*32) / 36 = 85.3334 grams