Question:

The reaction \(\mathrm{2N_2O_5(g) \rightarrow 4NO_2(g) + O_2(g)}\) follows first order kinetics. The pressure of a vessel containing only \(\mathrm{N_2O_5}\) was found to increase from 50 mm Hg to 87.5 mm Hg in 30 min. The pressure exerted by the gases after 60 min. Will be (Assume temperature remains constant) :

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Total pressure = P0 + 1.5 x (pressure of N2O5 consumed); find the half-life first.
Updated On: Nov 11, 2026
  • 106.25 mm Hg
  • 125 mm Hg
  • 116.25 mm Hg
  • 150 mm Hg
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The Correct Option is A

Solution and Explanation

Let the pressure of \(\mathrm{N_2O_5}\) consumed by time t be 2p. Then \(P_{total} = (50 - 2p) + 4p + p = 50 + 3p\).
At 30 min: \(50 + 3p = 87.5\), so \(p = 12.5\); \(\mathrm{N_2O_5}\) left = \(50 - 25 = 25\) mm Hg, half of the initial, so \(t_{1/2} = 30\) min.
At 60 min (two half-lives): \(\mathrm{N_2O_5}\) left = 12.5 mm Hg, consumed = 37.5 so \(2p = 37.5\), \(p = 18.75\).
\(P_{total} = 50 + 3(18.75) = 106.25\) mm Hg.
Answer: (1) 106.25 mm Hg
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