If the first two enthalpies are greater that the third, the overall D H soln will be positive and vice versa. The first two steps from above result in a positive D H, because it requires energy to break water's hydrogen bonding, and oil's dispersion forces. The third step does not counter this with a large negative D H, because there is little interaction between oil and water. Thus the D H soln is large and positive, so the reaction is not favored. Salts do dissolve in water, because they have a significant interaction with water resulting in a low D H soln .
Temperature effects the solubility of solutions.
Effects of solutions When a nonvolatile solute is added to a solvent, the vapor pressure of the solvent is lowered. Then understand that this caused less molecules of volatile solvent to be at the surface and less molecules evaporating. This decrease in vapor pressure as a result of the solution can help to explain the following colligative properties , properties that depend only on the number of molecules not he molecules themselves. When a nonvolatile solute is added to a solvent, the boiling point of the solution is higher than that of the pure solvent. Similarly, when a nonvolatile solute is added to a solvent, the freezing point of the solution is lower than that of the pure solvent.