Worked gas prob with my anwer +correct answer

[geffman1]

stoichiometric relationships

Homework Statement

hey guys just wondering if you could tell me where i went wrong
"One process related to formation of smog is:
2NO(g) + O2(g) 2NO2(g)
This reaction can be monitored in the laboratory by finding the total pressure of a mixture of the gases.

A bulb of volume 1.000 L is filled with a mixture of NO(g) and O2(g). The initial total pressure is 335 kPa at 26.4°C. After 6 hours the total pressure is 263 kPa. What mass of NO2(g) in grams has been formed? "

PV=nRT
P=335Kpa-263Kpa=72Kpa
R=8.314
v=1
t=299.4K

n=PV/RT=72/(8.314*299.4)=0.0289
Therefore mass =moles*molermass=0.0289*46.01=1.33grams HOWEVER answer is 2.66grams? therefore i should mulitple my answer by 2, but Y?
anyhelp would be apprecitated

Homework Equations

The Attempt at a Solution

 

[Borek]

If I understand what you did correctly, 72 kPa is amount of oxygen that reacted - take a look at the reaction equation now...