Dinitrogen pentoxide, N2O5, decomposes in the gas phase to form nitrogen dioxide, NO2, and oxygen gas, O2. The reaction is first order in dinitrogen pentoxide and has a half-life of 2.81 hours at 25 C. If a 1.5-liter reaction vessel initially contains 745 torr of N2O5 at 25 C, what partial pressure of O2 will be present in the vessel after 215 minutes?