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<a https://www.thestudentroom.co.uk/showthread.php?t=7467335'> Year 12s: what will be the first way you research your future options? >>
<a https://www.thestudentroom.co.uk/showthread.php?t=7467335'> Year 12s: what will be the first way you research your future options? >>
<a https://www.thestudentroom.co.uk/showthread.php?t=7467335'> Year 12s: what will be the first way you research your future options? >>

Chemistry HelP Kinetics..

I thought that the equilibrium postion shifts to the side with fewer moles when it comes to gases.. but this question and its mark scheme is throwing me off.. I'll link the attachment to the question below..
I picked option C as I figured the equilibrium position shifts to the left as it has fewer moles of gas.. and that it remained pale as the equilibrium position is now more towards the left.. so mixture is paler.. but the answer is A.. somehow.. i think its something to do with the fact that it said "the mixture is then allowed to stand" but I don't understand.. help:frown:
Screenshot 2022-01-29 124042.png64.8KB
Original post by Abraham_Otaku
I picked option C as I figured the equilibrium position shifts to the left as it has fewer moles of gas.. and that it remained pale as the equilibrium position is now more towards the left.. so mixture is paler.. but the answer is A.. somehow.. i think its something to do with the fact that it said "the mixture is then allowed to stand" but I don't understand.. help:frown:


You need to consider the two parts of the question 1) rapid pressure increase, and what that would do, then 2) mixture is allowed to stand, so what happened then (to the equilibrium, as you describe).

See https://edu.rsc.org/experiments/the-effect-of-pressure-and-temperature-on-equilibrium-le-chateliers-principle/1739.article
I've read it(and thanks) but it still doesn't make much sense.. I guess I understand that the concentration increases as for the same mole the volume of the gas is decreasing.. and so the equilibrium position shifts to the right.. but shouldn't the concentration of both gases increase? as opposed to just N2O4?..in which case with that logic shouldn't the equilibrium postion remain unchanged?? I feel like I'm misunderstanding something... and what about the fact that higher pressure favors the side with fewer moles?? does that not apply in this particular quesiton??(sorry for all the questions..)
Original post by Abraham_Otaku
I've read it(and thanks) but it still doesn't make much sense.. I guess I understand that the concentration increases as for the same mole the volume of the gas is decreasing.. and so the equilibrium position shifts to the right.. but shouldn't the concentration of both gases increase? as opposed to just N2O4?..in which case with that logic shouldn't the equilibrium postion remain unchanged?? I feel like I'm misunderstanding something... and what about the fact that higher pressure favors the side with fewer moles?? does that not apply in this particular quesiton??(sorry for all the questions..)

Think about the two parts of the question - when pressure is rapidly doubled, what happens? Even if it happens to both, what colour do you think it will go?

Then, when left to stand, it goes pale (as you said).
Original post by BlueChicken
Think about the two parts of the question - when pressure is rapidly doubled, what happens? Even if it happens to both, what colour do you think it will go?

Then, when left to stand, it goes pale (as you said).

ah I think I understand now, although it still confuses me, but I get it. Massive thanks bluechicken!:biggrin:
Original post by Abraham_Otaku
ah I think I understand now, although it still confuses me, but I get it. Massive thanks bluechicken!:biggrin:

Glad I helped, even if only a little bit. Equilibrium position movement is extremely confusing - you can easily get into a world where you can convince yourself both ways are correct!

Practice is key, as 1) it will become more familiar and hopefully reduce the confusion, and 2) similar style questions come up all the time (even the same reactions), so understanding what the question is asking is key.

Good luck!

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