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The book states the solution which shows large positive deviation from Raoult's Law form minimum boiling azeotrope What is meant by " minimum boiling azeotrope" or I should say what does minimum signify here

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  • $\begingroup$ I think the meaning is very clear from the attached figure. A minimum boiling azeotrope boils at lower temperature than any other mixing composition of the two compounds. $\endgroup$ – Tyberius Apr 29 '20 at 17:59
  • $\begingroup$ I wanted the reason as well and Max w has done it lots of thanks $\endgroup$ – Anusha Apr 30 '20 at 19:07
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What is meant by minimum boiling azeotrope?

Two red lines have been drawn in the phase diagram below. Both are parallel to the horizontal axis. The first is at the boiling point of ethanol, and the second is at the boiling point of water.

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Now look at the liquid curve.

(1) As the % Water increases from 0% the curve starts down, outside of the zone defined between the two red lines. The curve can't go down forever since at 100% water the curve must reach 373 K. So between 0% Water and 100% Water there must be a minimum in the curve.

(2) Since the curve falls below the zone defined between the two red lines an azetrope must form at the minimum. Remember that if the liquid is changing composition so must the vapor.


The converse is true too. If the vapor line goes above the zone defined between the two red lines, then a maximum boiling azeotrope must form.

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