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Solution Formation

APCHEM-N5TAHG

The Børn-Haber cycle was developed as a means to explain the concept of lattice energy for ionic compounds, but it can also be applied to describe the energetics of solution formation. It is especially useful in the case of dissolution of ionic solids in water. We can envision solution formation as being the net result of a three-step process:

(1) The solvent expands, making space for the solute particles.
(2) The solute's IMF have to be overcome, freeing the individual ions or molecules from each other.
(3) Solute and solvent particles (molecules, ions) attract each other, forming the solution.

Consider the case of an ionic solid, MX dissolving in water, as shown by the equation:

$${ MX(s)\rightarrow { M }^{ + } }(aq)+{ X }^{ - }(aq)$$

Select the choice below that is INCORRECT concerning formation of this solution.

A

Steps (1) and (2) are both endothermic.

B

Step (3) must be exothermic, or a solution will not be formed.

C

The overall enthalpy of solution, $\Delta { H }_{ solution }$, must be negative (exothermic).

D

The entropy of solution, $\Delta { S }_{ solution }$, must be positive.