Question

If the partial pressure of hof in a 1.00-L flask is initially at 25 °C, what are the total pressure in the flask and the partial pressure of after exactly 35 minutes? After 57 min?

Answer 1

solution :-

half life = 35 min

rate constant K = 0.693 / half life

                        = 0.693 / 35 min = 0.0198 min-1

Lets assume initial pressure is 1 atm

So after 35 min half of the HOF will be converted to HF and 1/2O2

So the partial pressure of the HOF after 35 min is = 1 atm / 2 = 0.5 atm

Partial pressure of the HF = 0.5 atm

And partial pressure of the O2 = ½ * 0.5 = 0.25 atm

Total pressure after 35 min = sum of partial oressures

                                                 = 0.5 atm + 0.5 atm 0.25 atm

                                                = 1.25 atm

Now lets calculate the partial pressures and total pressure after 57 min

Lets calculate the partial pressure of the HOF after 57 min

Ln (P2/P1) = - k*t

Ln (P2/1 atm) = -0.0198 min-1 * 57 min

Ln (P2/1 atm) = -1.1286

P2/1 atm = anti ln [-1.1286]

P2/1 atm = 0.323486

P2 = 0.323486 * 1 atm

P2 = 0.3235 atm

So the partial pressure of the HOF after 57 min = 0.3235 atm

Now lets calculate the partial pressure HF = 1 atm – 0.3235 atm = 0.6765 atm

Partial pressure of O2 = ½ * 0.6765 atm = 0.338 atm

Now lets calculate the total pressure

Total pressure = 0.3235 atm + 0.6765 atm + 0.338atm = 1.34 atm