Limiting Reactants Problem?

Question

Acid rain can form from the combustion of nitrogen gas producing HNO3(aq) in a two-step process.
N2(g) + 2O2(g) → 2NO2(g)
3NO2(g) + H2O(g) → 2HNO3(aq) + NO(g)

a. A car burns 420. g of N2 according to the above equations. Howmany grams of HNO3 will be produced?

b. For the above reactions to occur, O2 must be in excess in the first step. What is the minimum amount of O2 needed in grams?

c. What volume does the amount of O2 in part b occupy if its density
is 1.4 g/L?


I don't get it. If you can help, thanks a ton !
much help appreciated ! :D

Answer 1

To start, convert 420 grams to g-moles. Since N2 has a "mole weight" of 28, you have 15 moles.

Following through the equations, 15 moles of N2 can create 30 moles of NO2, which in turn, can create 20 mole of HNO3. So multiply the mole weight of HNO3 by 20 to get part a.

From the first equation, 15 moles of N2 require at least 30 moles of O2 to produce the maximum anount of NO2. So multiply 30 moles of O2 by its mole wt of 32.

Take the mass computed above and divide by 1.4 g/L. This gives the volume in liters.