To calculate the total pressure in the flask, we need to convert all the partial pressures to the same unit and then add them together. We can convert the partial pressures of oxygen and ammonia to atm using the following conversions:
1 atm = 760 torr
1 atm = 101.325 kPa
Partial pressure of oxygen in atm = 643 torr / 760 torr/atm = 0.846 atm
Partial pressure of ammonia in atm = 2865 kPa / 101.325 kPa/atm = 28.27 atm
Now we can add up all the partial pressures in atm:
Total pressure in atm = Nitrogen partial pressure in atm + Oxygen partial pressure in atm + Ammonia partial pressure in atm
Total pressure in atm = 9.84 atm + 0.846 atm + 28.27 atm
Total pressure in atm = 38.956 atm
Therefore, the total pressure in the flask is 38.956 atm (rounded to three decimal places).