The sign of the molar heat of solution (whether it is endothermic or exothermic) of a solid solute in a liquid solvent depends the relative values of AH° for three steps in the dissolution process: (1) separation of the solute molecules, (2) separation of the solvent molecules and (3) mixing of solvent and solute molecules. Two of these steps are always endothermic, while the third is always exothermic. Which of the following statements is true? A) Separation of the solvent molecules is exothermic while separation of the solute molecules is endothermic. B) Mixing of the solvent and solute molecules can be exothermic or endothermic. C) If the magnitude of either separation step is greater than the magnitude of the mixing step, then molar heat of solution will be negative. D) If the magnitude of the sum of the two separation steps is greater thạn the magnitude of the mixing step, then molar heat of solution will be positive. E) The molar heat of solution is always negative. How does the solubility of an ionic compound in a liquid solvent vary with temperature?
1.) To explain which of the following statement is true for molar heat of solution during dissolution process.
Three steps in the dissolution process
1) separation of the solute molecules,(endothermic)
2.) separation of the solvent molecules, (endothermic)
3.) mixing of solvent and solute molecules (exothermic)
the sign of molar heat of solution can be positive or negative, which depends on :
- if more energy is required for separation of solute and solvent molecules.
- if more energy was released on mixing of solute and solvent molecules.
Now, the overall process is exothermic (negative) if more energy is released in mixing of solvent and solute molecules than is used in separation of solute and solvent molecules. The overall process in endothermic (positive), if more energy is used in separation of solute and solvent molecules than is released upon mixing of solute and solvent molecules.
Thus, we can say that if the magnitude of the sum of the two separation steps is greater than the mixing step, then molar heat of solution will be positive.
Hence, option D) is correct.
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