Unit 2 Gases Question

[Wizard]

Hey guys

I was just doing the 2008 chemology trial exam (which by the way is riddled with errors, and is possibly the worst trial exam ever) and this question came up:

Two vessels (Vessel A and Vessel B) are connected to each other by a valve, which is closed. In flask A, there is a Volume of 200ml, and a pressure is 2 atm. In Vessel B, the Volume is 800ml and the pressure is 1.4 atm. The volume is kept constant. If the tap is opened, and the contents of the vessels were allowed to mix, the total pressure would be:
(a) 0.5 atm
(b) 2.0 atm
(c) 3.6 atm
(d) 0.4 atm
Answers say 0.4, but why? 
Thanks

[shinny]

I really can't remember my unit 2 stuff so hopefully this is correct.

[Wizard]

Thanks, I see how to get that answer now.
The thing I am confused with though is why isnt the 800 ml vessel included in the calculation?

[nerd]

Because you are MIXING the two vessels, that essentially means you are pouring the volume of one into the other. Hence, you add the extra volume (200mL) to the original volume (800mL) to get the final volume of 1000mL

[dekoyl]

I really can't remember my unit 2 stuff so hopefully this is correct.

shinjitsuzx are you saying unit 2 stuff won't be very relevant in units 3 and 4?

If so.. oh am I so glad.

[shinny]

Depends what really. Some of it is assumed knowledge if its RELEVANT (e.g. the question just then could easily be asked in unit3 if they really wanted to) but be thankful you don't have to remember all that crap about Dalton and the different models and the sub-shells from unit 1. I had about 5 friends drop chem within the first week due to that crap -_-" But yeh, everything that came up in chem this year was relevant strictly to units 3/4. However, I'd probly watch out since spesh this year had some stuff from general maths and VCAA does seem to be backtracking a bit to screw people over.

[dekoyl]

Ahh okay thanks for the heads up