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Answer for both are D:

Can someone please explain them!
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lionike123
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As it is being cooled La Chatliers Principle states that the system would oppose change. Cooling it to 250 means decreasing the temperature and this means the system will oppose the change and move in the forward direction meaning it would go darker. By Compressing it it means they are increasing the pressure. By increasing the pressure, the position of the equilibrium would favour the side with fewer moles which is the I2 therefore it goes purple.
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(Original post by lionike123)
As it is being cooled La Chatliers Principle states that the system would oppose change. Cooling it to 250 means decreasing the temperature and this means the system will oppose the change and move in the forward direction meaning it would go darker. By Compressing it it means they are increasing the pressure. By increasing the pressure, the position of the equilibrium would favour the side with fewer moles which is the I2 therefore it goes purple.
I understand part a), thanks!

In the reaction, don't both sides have the same number number of gas molecules, so where does the equilibrium shift?
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Rauhan
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ok so for the first one in the question it says that the equilibrium mixture was allowed to reach 300 degrees and because its a dynamic equilibrium so when its cooled the reaction will favour the backward direction, therefore, making more of the reactants and u will see a purple solution cuz iodine has a purple colour and hydrogen is colourless
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lionike123
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Look clearly the HI has 2 and the H2 AND I2 has 1 each. It cant go colorless to colorless so it has to go from colorless to purple.
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(Original post by lionike123)
Look clearly the HI has 2 and the H2 AND I2 has 1 each. It cant go colorless to colorless so it has to go from colorless to purple.
Thanks!

Can you please just explain this last one?

i really appreciate the help!


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HydraFly
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(Original post by Mark jam)
I understand part a), thanks!

In the reaction, don't both sides have the same number number of gas molecules, so where does the equilibrium shift?
A)
There is no pressure effect in this case; I am assuming you have covered Kc. A simple idea is that the exothermic reaction is favoured, hence forward reaction is prefered (eq. shifts to right).

B)
Hm... Are you sure?
Code:
Effect of Pressure- If pressure  is increased then equilibrium will shift in the direction where volume is decreased.
When number of moles on either side of a equation is the same, then there is no effect of change of pressure on equilibrium

That is specific to that reaction.... If anything, gas laws suggest an increase in temperature, so in fact it would shift to the left... Hm....
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HydraFly
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(Original post by lionike123)
Look clearly the HI has 2 and the H2 AND I2 has 1 each. It cant go colorless to colorless so it has to go from colorless to purple.
At equilibrium it wouldn't be colourless... It still has I2 present...
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HydraFly
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Oh wait... Could it be because all the I2 molecules are closer together for a moment that it physically appears darker?? The question does say 'immediately'
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(Original post by Mark jam)
I understand part a), thanks!

In the reaction, don't both sides have the same number number of gas molecules, so where does the equilibrium shift?
Yes I think you are right - therefor from a pressure point of view it has no effect on the equilibrium position.

However increasing the pressure brings particles closer together which results in increasing the concentration of all particles - but this also has no effect on equilibrium position! One might say 'A' could be the answer 'no visible changed' as the equilibrium position is not affected, but it would be wrong:

The purple molecules are concentrated together making the colour more intense.

A horrible trick question that has nothing to do with equilibrium and more of a physical thing that I bet would be no where to found on the syllabus.

I'm not 100% sure of the above, hopefully someone can confirm. I think Hydrafly said something similar
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