Chemistry Predictions/Thoughts (2 Viewers)

[coolcat6778]

View attachment 50483

i was doing this worksheet and found this. Specifically looking at part e, i just remember there was a similar question in the hsc.

can someone tell me how equilibrium can shift but the reaction quotient doesnt?

if this is right i get 2 extra marks

 

[C2H6O]

can someone tell me how equilibrium can shift but the reaction quotient doesnt?

if this is right i get 2 extra marks

Cause some change caused concentrations to change so that Q≠K, then it shifts back so that Q=K

 

[coolcat6778]

so do we all agree temperature changes?

 

[Luca26]

View attachment 50483

i was doing this worksheet and found this. Specifically looking at part e, i just remember there was a similar question in the hsc.

The worksheet answers are wrong.

(e) Adding Ar is not a disturbance within the meaning of that term in Le Chatelier's Principle. This was also the point the HSC question is testing.

(a) is also a common mistake. As written, the answer to (a) is that any change in the position of equilibrium cannot be determined without knowing how the pressure change was achieved.

• If the pressure was increased by the system being compressed (so volume decreased), then it is a disturbance and will cause a shift to favour fewer gaseous molecules and so a move to favour the reactants (in this case). The value of K will not change.
• If the pressure was increased by adding an inert gas (like in (e)), then it is not a disturbance and so no change occurs in position or in K.
• If the pressure was increased by heating the system, then this is a disturbance that favours the endothermic reaction, and so the position shifts to the right and the value of K increases.

All the confusion about the HSC argon question and arguments about pressure change reflect a misunderstanding of Le Chatelier's Principle. There is only a shift following a disturbance and a pressure change may or may not be a disturbance depending on how it comes about. If the pressure change is not caused by a disturbance to the system, then it is irrelevant to Le Chatelier's Principle considerations.

 

[C2H6O]

so do we all agree temperature changes?

For this years chem question? No it doesn’t unless Gay lussac’s applies

 

[lolcti]

Good luck everyone!!!!

 

[lolcti]

Wait bruh this is the wrong one woops I meant that for physics

 

[Luca26]

For this years chem question? No it doesn’t unless Gay lussac’s applies

In Chemistry, Gay-Lussac's Law concerns the volume ratios in which reactions occur at constant pressure and temperature. There is no reaction occurring involving argon, so this law is irrelevant.

Physics books sometimes describe a pressure / temperature relationship as Gay-Lussac's law, which is also sometimes called Ammontons' Law. Gay-Lussac's research in this area was actually looking at volume and supports what is called Charles' Law in Chemistry.

Even if the pressure varies in direct proportion to absolute temperature law is what is meant y Gay-Lussac's Law in above posts, it is not applicable to this system as it reflects pressure changes for a given sample of gas at constant volume,; as such, it requires a constant gas sample in terms of moles of gas / number of gaseous molecules. The pressure increase here follows directly from the added argon, so the gas composition is changed and the conditions for applying the law are not met. The Ideal Gas Law Model makes this clear, in that a k% increase in moles results in a k% increase in pressure when volume and temperature are unchanged.

I can't see any way for even the Physics version of Gay-Lussac's Law apply.