Expert: Scotto - 12/2/2008

Question
Hydrazine, N2H4 and hydrogen peroxide, H2O2, have been used as rocket propellants. They react according to the equation: 7H2O2 + N2H4 ---> 2HNO3 + 8H2O

A. How many moles of hydrogen peroxide are needed to produce 500 grams of nitric acid?

B. How many liters of water are produced from the complete reaction of 75 moles of hydrazine in excess peroxide?

C. If 500 grams of peroxide are reacted with 500 grams of hydrazine, what is the theoretical yield of nitric acid?

Answer
The molecular weights of one mole of each of the following is given:
34.01 grams for Hydrogen Peroxide,
32.05 grams for Hydrazine,
63.01 grams for Nitric Acid, and
18.02 grams for Water.

A.  500 grams of nitric acid is 500/63.01 moles of nitric acid.
Since the equation produces 2 moles of nitric acid out of 7 moles of hydrogen peroxide, calculate the moles of nitric acid produced (500/63.01) and multiply it by 7/2 to get the moles of hydrogen peroxide.  The calculation is the (500/63.01)(7/2) = 3500/126.02.  You can do that on a calculator.

B. The 75 moles of hydrazine produce 8*75 moles of water.  That can be done in your head since to multiply by 75 is the same as taking 8*100 and finding 3/4ths.

C. 500 grams of peroxide is 500/34.01 moles of peroxide.
500 grams of hydranzine is 500/32.05 moles of hydranzine.
You can do it exactly on a calculator, but it's approximately 15 moles of each.  If we have about 15 moles of hydrogen peroxide, we only need about 15/7 moles of of hyrazine.

Using the weights given and doing the calculations on a calculator exactly.  The answer should be somewhere near 7.5 moles of nitric acid and around 30 moles of water.  Since we have too many moles of Hydrazine, there will be some left over, but all of the grams of hydrogen peroxide will be used.