A) When calcium hydroxide (Ca(OH)2, M = 74.09 g/mol) is dissolved in water at T

Question

A) When calcium hydroxide (Ca(OH)2, M = 74.09 g/mol) is dissolved in water at T = 25.0 C, the temperature of the water increases. Based on this observation, would you expect the solubility of calcium hydroxide in water to increase, decrease, or stay approximately constant when the initial temperature of the water is changed to T = 75.0 C? Justify your answer.

B) At T = 373. K the vapor pressure of pure 1,2 dibromoethane (E) is pE* = 338. torr, and the vapor pressure of pure 1,2 dibromopropane (P) is pP* = 214. torr. The total pressure above a liquid solution of 1,2 dibromoethane and 1,2 dibromopropane at T = 373. K is ptotal = 292. torr. Assuming these two liquids form an ideal solution, what is the value for XE, the mole fraction of 1,2 dibromoethane in the solution?

Explanation / Answer

A) When calcium hydroxide (Ca(OH)2, M = 74.09 g/mol) is dissolved in water at T = 250 C, the temperature of the water increases.

But, the solubility of calcium hydroxide in water decreases,when the initial temperature of the water is changed to T = 750 C.

the reason is given below.

for (Ca(OH)2, , the dissolution and solvation process is an exothermic equilibrium. and an increase in the temperaure of the reaction drives the equilibrium in reverse and favours crysalisation.

in practice, the emperaure can effect the entropic term, but also the enthalpies of the Crysal lattices,the heats givenout by the solute-solvent ineractions etc. it is the balance of this process that determines the solubility of the crystal, in general.

in the case of (Ca(OH)2, dissolved in waer, as the temperaure is increased then the solubiltiy decreases.

there is an equilibrium betweenC rysallisation and dissolution+ solvation .

an increase in the temperature of the reaction drives the equilibrium in reverse and favours crysalisation rather han forward reaction. this is simply an enthalpic term.which follows LECHAtLIER'S PRINCIPLE.

the equation is an equilibrium.

Ca(OH)2 + H2O = Ca+2 + 2 OH- + dela

it is an exothermic reaction. at a particular temperaure, a paricular amount of heat is evolved.

as the temperature is incresed, the heat conen of the syatem increases and more thrust is there on the right hand side of the equlibrium.

hence, by  LECHAtLIER'S PRINCIPLE. the system would consume some of the heat and the equiolibrium shifts towards left hand side of the equilibrium to reduce he stress and thereby favours crysallisation.

B) At T = 3730 K,

the vapor pressure of pure 1,2 dibromoethane (E) is pE* = 338. torr,

and the vapor pressure of pure 1,2 dibromopropane (P) is pP* = 214. torr.

The total pressure of he liquid solution of 1,2 dibromoethane and 1,2 dibromopropane is ptotal = 292. torr.

if these two liquids form an ideal solution,

an ideal mixure of liquids obeys RAOULS LAW.

he wo liquids form an ideal mixure.

the patrial vapour pressure of a liquid in a mixture is equal to the vapour pressure of that liquid in its pure form multiplied by its mole fraction.

PE + PP = PtOtAL

AND

XE + XP = XtOtAL

HEN AS PER RAOUL'S LAW

PE * XE + PP * XP = PtOtAL* XtOtAL

338* XE + 214* XP = 292* XtOtAL

HEN

PE * XE = POAL * XOAL -  PP * XP

HEN

XE = (POAL * XOAL -  PP * XP )   / PE

XE = (POAL * (XE + XP) -  PP * XP )   / PE

HEN

338* XE + 214* XP = 292* (XE + XP)

46* XE = 78* XP

HEREFORE, XE = 1.7* XP

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