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Topic: CaCO3 --> CaO + CO2  (Read 34332 times)

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CaCO3 --> CaO + CO2
« on: November 11, 2005, 09:38:25 AM »
Hi, I'm an italian student in medicine, firts year. Today I had an examination on chemistry, and a question was:

Is better to have the reaction
CaCO3 --> CaO + CO2
in a close recipient or in a open recipient/space?

I answered in a close recipient, because of Le Chatelier principle, the temperature neeeded, and because in a close system you can actually remove the CO2, eliminating the problem of the CO2 pressure, but some other people answered   differently, in open recipient, because of the CO2 pressure. The tutors who will correct the examination told someone the open recipient was the correct answer, but they were doubtfull too.
I'm on my way, I think mine is correct.
Sorry for my english and for the question if under your forum level, ...
Thank you for paying attention
If anyone will give me a reply...
Thank you very much!

Online Borek

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Re:CaCO3 --> CaO + CO2
« Reply #1 on: November 11, 2005, 10:22:57 AM »
Is better to have the reaction
CaCO3 --> CaO + CO2
in a close recipient or in a open recipient/space?

Not sure if I understand you correctly, but if the question is about CaCO3 decomposition - it should be roasted in open. This way CO2 will go away an the reaction proceeds easier.
« Last Edit: November 11, 2005, 10:23:20 AM by Borek »
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Re:CaCO3 --> CaO + CO2
« Reply #2 on: November 11, 2005, 01:20:38 PM »
sorry for my english, it was not a sistem,but just a recipient. and the question was: better in or out to have the decomposition completed?
I though that out it'll not complete all the transformation of CaCO3 because of the presence of the CO2 in the air, but if it was in the recipient you can take away part of CO2 time after time untill the CaCO3 will be completely transformed, even tough it's more difficult to do. But i tough just in this way you could have all the CaCO3 transformated, out of the recipient instead i tough a minimal part of CaCO3 will never transform because of Le Cathelier principle...
what do you think?

Offline jdurg

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Re:CaCO3 --> CaO + CO2
« Reply #3 on: November 11, 2005, 02:31:42 PM »
If the reaction takes place in a closed vessel, after a while the CO2 concentration will build up and push the equillibrium to the left in order to relieve the pressure.  What will then happen is that less CaCO3 will decompose, and some of the CaO that has formed will react again with the CO2 in order to relieve the pressure.  If the presence of CO2 in the open atmosphere was a concern, then how come houses and forest can burn completely when that reaction also has CO2 as a product?   ;)

As no reaction conditions are given for your experiment, that means that it must have taken place under standard temperatures and pressures.  The volume of air in the Earth's atmosphere is so great that the CO2 concentration will never build up high enough to alter the reaction as given.  In a closed vessel, the concentration WILL build up and thusly slow your reaction.

An open reaction vessel implies that there are no limits in regards to the atmospheric volume and that there is a constant changing of the air.  A closed vessel implies that there IS a limit to the volume in there and that there is no changing of the air.  If you open up the box to remove CO2, then you're turning it from a closed system into an open system.

To properly think about this, let's say you take one pile of CaCO3 and put it in a glass jar which is sealed completely shut by melting it closed.  You then take another pile and place it on the table next to the sealed jar.  Which pile will decompose more readily?   ;D
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