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Chemistry: Post your doubts here!

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Metallic9896

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zellyman said:
I think its D
Draw the chain first,you can see that the ammoniacan first react with the C-Br bonds of the 1st carbon and that of the 5th carbon (in the straight chain) which forms the ring as shown.
Sorry if I'm being unclear >_<
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Haha no, thanks, it makes sense. :)
 
Metanoia

Metanoia

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Metallic9896 said:
Hmm if the solution does form that means water molecules felt more comfortable forming bonds with the anhydrous aluminium chloride than they did with themselves. All systems want to achieve a lower and lower energy state that gives out heat so they become more stable. If they DID like forming bonds with anhydrous aluminium choride, this means that the energy released when they formed these bonds was MORE than the energy needed to break the water molecules' bonds with themselves, which means that there was a net release of energy, i.e. reaction was exothermic, not endothermic. That leaves only C as the correct choice cause all other options contain statement 1 and we just got rid of it. Without even thinking about 2 and 3 you can choose C. But, you should know about 2 and 3 from the book and the chapter of periodicity where we are told to know reactions of water and period 3 chlorides. Hope I helped. :)

EDIT: Anything that successfully dissolves, you can be sure it's an exothermic process.
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This is a good explanation. I would like to add to the last sentence.

"Anything that successfully dissolves, you can be sure it's an exothermic process."

There are some substances that dissolve and are endothermic (e.g. dissolving ammonium chlorides), a spontaneous reaction does not only depends on enthalpy changes but also entropy and the temperature.
 
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Metallic9896

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Metanoia said:
This is a good explanation. I would like to add to the last sentence.

"Anything that successfully dissolves, you can be sure it's an exothermic process."

There are some substances that dissolve and are endothermic (e.g. dissolving ammonium chlorides), a spontaneous reaction does not only depends on enthalpy changes but also entropy and the temperature.
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Of course, I only said that because it's AS tomorrow and didn't want to confuse the target audience who will be giving P1 tomorrow while entropy is part of the A2 syllabus so I'm sure CIE won't ask any questions that would relate to that area. But yes what you said is absolutely true. :D
 
xnamexname

xnamexname

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sarmadimran said:
anyone plz
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Is it a D?
If so you need carbon dioxide which comes from thermal decomposition of group 2 carbonates
the harder it is to decompose the carbonate the lesser the amount of CO2 produced
So thermal stability increase down the group so carbonate with most magnesium will decompose at lower temperature making it more effective followed by calcium and finally barium
 
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Metallic9896

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Zaki ali asghar said:
Same here dude was thinking would get 40 right after paper was done,ended up doing silly mistakes. :/
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Ik man very frustrating realization, stupid mistakes like misreading the question or not reading it carefully *facepalm* nothing I got wrong so far was a conceptual mistake, all due to nonesense mistakes.
 
Mstudent

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darks said:
For Kc do not consider solid and you should get correct answer!
Good Luck! It was easy for us!
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But the other substances are gases, so could you plz write the steps for me cuz I am VERY confused, and very tense about my exams 3 hours later!
 
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Mstudent said:
But the other substances are gases, so could you plz write the steps for me cuz I am VERY confused, and very tense about my exams 3 hours later!
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Sure.
I think you have reached moles at equilibrum for NH3 and HCL to be 0.7.
so Kc=[NH3][HCL]
vol. is given.
Kc=[0.7/0.5][0.7/0.5]=C
 
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