[Araconan]

I am currently attempting the following problem:

Consider the flask diagrammed below. What are the final partial pressures of H2 and N2 after the stopcock between the two flasks is opened? (Assume the final volume is 3 L) What is the total pressure in torrs?

_________                        _____________
l                l                         l                       l
l  2L H2     l--------l----l---- --l  1L   N2          l
l  475 torr l--------l----l-------l   0.2 atm        l
l                l                         l                       l
l________l                         l___________ l

Note: The thing in the middle is the stopcock

My attempt:

Dalton's Law states that the total pressure is the sum of the individual pressures of the gases as if they were in separate containers.
So the individual pressure of the 2 litres of H2 would be 475 torrs and the individual pressure of the 1 litre of N2 would be 0.2 atm (converting to torrs would be 0.2*760=152 torrs)
Hence the total pressure would be the sum of the two, so 475 + 152 = 604 torrs. And the partial pressures would be 475 torrs for H2 and 152 torrs for N2.
However, this differs from the actual answers. So what am I doing wrong?

Thank you in advance!

[Borek]

Imagine left tank was initially completely empty - what would be the final pressure of the nitrogen after stopcock was opened?

Do you understand that what you calculated is the partial pressure of nitrogen regardless of initial content of the left tank?

[Araconan]

Ahh I forgot about the changing volume. Seems like my brain wasn't working yesterday hehe