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Equilibrium (water and ethanol)

  • Thread starter ND3G
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Ethanol and water are completely miscible; that is, they dissolve in each other in all proportions

a) When two substances are mixed, is randomness increased or decreased?

b) Heat is liberated in the disolving process. Does the tendency toward minimum energy favour the seperated pure substances, or the solution of one in the other?

c) In view of the tendencies listed in (a) and (b) above, explain why water and ethanol are completely miscible.


This question as been asked before but the replies do not all agree with each other.

https://www.physicsforums.com/showthread.php?t=74957

and

https://www.physicsforums.com/showthread.php?t=65859

For those of us that are a little confused, can someone please clarify the situation? (BTW this is for grade 12 Chemistry. They are looking for basic answers not forumulas...)

My take is:

a) When changes occur in a system particles are more likely to achieve a disordered condition than an ordered one. Therefore, randomness is increased.

b) The tendency towards minimum energy favour the solution of one in the other.

My reason for this is: Since heat is liberated this lowers the energy of the solution. The systems answer to the mixing of the solutions is not to unmix them but to release heat. The heat and therefore randomness of the surrounds increase.

c) By answer to part c whould then be that both processes favour the mixing of the two products as long as the system is not a closed one.
 
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Answers and Replies

  • #2
chemisttree
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Good answer!

Concerning GCT's response that the mixing is actually a decrease in entropy, I don't believe that entropy is decreasing.
 

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