Verified Solution • 2025–26 Session moderate

QJEEM18Ch84f2: JEE Main 2018 Chemistry - Class 12 JEEM18Ch84f2 Solution: N 2 O 5 decomposes to NO 2 and O 2 and follows first order…

N2O5 decomposes to NO2 and O2 and follows first order kinetics. After 50 minutes, the pressure inside the vessel increases from 50 mmHg to 87.5 mmHg. The pressure of the gaseous mixture after 100 minute at constant temperature will be :

Multiple Choice Options

  • A 175.0 mmHg
  • B 116.25 mmHg
  • C 136.25 mmHg
  • D 106.25 mmHg

Step-by-Step Verified Solution

N2O5 ⇌\rightleftharpoons 2NO2 + 12{1 \over 2} O2
At t = 0 50 0 0
At t = 50 min 50 −- P1 2P1 P12{{{P_1}} \over 2}


Total pressure after 50 min,

= 50 −- P1 + 2P1 + P12{{{P_1}} \over 2} = 87.5

∴   \therefore\,\,\, 50 + 3P12{{3{P_1}} \over 2} = 87.5

⇒\Rightarrow    \,\,\, P1 = 25

So, 50 min is the Half −- life period of the reaction.

Then 100 min is two half life

N2O5 ⇌\rightleftharpoons 2NO2 + 12{1 \over 2} O2
At t = 100 min 50 −- P2 2P2 P22{{{P_2}} \over 2}


∴   \therefore\,\,\, 50 −- P2 = 252{{25} \over 2}

P2 = 37.5

∴   \therefore\,\,\, Total pressure at t = 100 min

= 50 −- P2 + 2P2 + P22{{{P_2}} \over 2}

= 50 + 32{3 \over 2} ×\times 37.5

= 106.25 mm of Hg

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