Question

Nitrogen and oxygen react to form nitric oxide (NO). All substances are in the gas phase. If 0.352 atm of nitrogen and 0.511 atm of oxygen react, what is the partial pressure of nitric oxide (in mmHg) when this reaction goes 73.9 complete. The temperature and volume are constant.

Answer 1

I assume you mean 73.9% complete.
N2 + O2 ==> 2NO
This is a limiting reagent (LR) problem. First we determine the LR.
atm NO formed if we used all of the N2 and an unlimited supply of O2.
0.352 atm N2 x (2 mols NO/1 mol N2) = 0.352 x 2/1 = 0.704 atm NO produced.

atm NO formed if we used all of the O2 and an unlimited supply of N2.
0.511 atm O2 x (2 mol NO/1 mol O2) = 1.022 atm NO produced.

You can see these two answers don't agree so one of them must be wrong. In LR problem, the correct value is ALWAYS the smaller value and the reagent producing that value is the limiting reagent. Therefore, N2 is the limiting reagent and we will produce 0.704 atm NO at 100% yield. Since this is only 73.9% yield the product will be 0.704 x 0.739 = ?.