3.54 × 10⁵ Pa.
Ammonia NH₃ and oxygen gas O₂ reacts at a one-to-one molar ratio to produce NO and H₂O.
NH₃ + O₂ → NO + H₂O (Balanced)
The vessel will contain
It will contain 0.3841 + 0.2031 + 0.2031 = 0.7903 mol gas particles by the end of the reaction.
[tex]P = n \cdot R \cdot T / V \\\phantom{P} = 0.7903 \times (8.314 \times 10^{3}) \times (273 + 23) / 5.50 \\\phantom{P} = 3.54 \times 10^5 \; \text{Pa}[/tex]
Assuming that the final mixture is an ideal gas, it will exert a pressure of 3.54 × 10⁵ Pa on the container.