[kineticwave]

Flask A has a volume of 2L and contains SO2 at a pressure of 7.5kpa. Flask B has a volume of 1L and contains excess F2 and at unknown pressure. Both flasks are at 300K. When the stopcock separating the two flasks is opened, the reaction SO2 + F2 -> SO2F2 occurs completely and the final pressure is found to be 7.5kpa at 300K. What was the initial pressure of F2 in flask B?

[Borek]

You have to show your attempts at solving the question to receive help. This is a forum policy, described in the forum rules.

[kineticwave]

Sorry, I've tried using the P1V1 = P2V2 method to find the pressure of SO2 then subtracting from the final pressure given to get the pressure of F2. But then somehow the answer comes to 22.5 kpa which apparently is because you have to find the P2 of the gases before they react but just after mixing. I'm not sure how to do that though.

[fledarmus]

You can't just use P1V1+P2V2, because you also have a change in the number of moles of gas due to your reaction.

Start at the end - what is the total volume of your system? What is the temperature? What is the pressure? So how many moles of gas are there after the reaction is complete? Then work your way backwards.

[kineticwave]

Ah, thank you, but my prof didn't work on it backwards. And I was wondering how you would go about this question going forward along with the reaction.