Final answer:
To calculate the total pressure of the gases in the flask after 1.5 hours for the gas-phase reaction of N2O5, we use the first-order rate law to find the pressure of N2O5 at that time, and then apply the ideal gas law to determine the total pressure.
Step-by-step explanation:
The question involves a first-order, gas-phase reaction of dinitrogen pentoxide (N2O5) decomposing into nitrogen dioxide (N2O4) and oxygen (O2). The half-life for the disappearance of N2O5 is given as 3,240 seconds. To calculate the total pressure in the flask after 1.5 hours (which is 5,400 seconds), we must apply the concept of first-order reaction kinetics. The integrated first-order rate law can help determine the concentration (or pressure) of N2O5 at any given time. Then, using the ideal gas law, we can find out the partial pressures of the products formed, and hence, the total pressure in the flask.