Question

HOF-->HF + 1/2O2(oxygen)
Half life: 30 minutes
If the partial pressure of HOF in a 1.00 L flask is initially 100 mm Hg at 25C, what is the total pressure in the flask and the partial pressure of HOF after exactly 30 minutes?

Answer 1

Half of it is gone.

So at t=0, pressure was 100
so at t=30, partial pressure is 50mmHg, total pressure is 5/2 of 50mmHg.
That is the amount of HOF converted to HF and 1/2 O2, added to the remaining 50mmHg.

Answer 2

I would approach the problem by setting up an ICE chart. In exactly 30 minutes, 1/2 of the HOF will remain, 1/2 will have formed HF and 1/2 of the HF will be O2. Total pressure = sum of partial pressures.