Question

Dinitrogen pentoxide decomposes in the gas phase to form nitrogen dioxide and oxygen gas. The reaction is first order in dinitrogen pentoxide and has a half-life of 2.81 h at 25 ∘C.

If a 1.4-L reaction vessel initially contains 760 torr of N2O5 at 25 ∘C, what partial pressure of O2 is present in the vessel after 220 minutes?

Answer 1

half-life t1/2 = 2.81 h = 168.6 min

rate constant k = 0.693 / t1/2

                          = 0.693 / 168.6

                          = 0.00411 min-1

2 N2O5 (g) ----------------------> 4 NO2 (g) + O2 (g)

760 - 2x       4x    x

k = 1/t ln (Po / Pt)

0.00411 = 1 / 220 ln (760 / 760 - 2x)

x = 226

P O2 = x = 226 torr

partial pressure of O2 is = 226 torr