solutions and solubility

Because the ion dipole interactions are much stronger

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because the ion-dipole interactions are much stronger than the hydrogen bonds that occur in water, the heat of hydration is always a largely negative (exothermic) number for ionic compounds - energy is released as the resulting solution is much more stable than the previously isolated solute and solvent for ionic compounds the heat of hydration is the negative of the solute's lattice energy ( heat of hydration = - lattice energy (the energy released when a solid lattice forms )) we can write the enthalpy of a solution as just the sum of two terms, one endothermic and the other exothermic for an ionic aqueous solution the overall enthalpy of the solution depends on the relative magnitude on the enthalpy of the solute and the heat of hydration. There are three possible scenarios for a solution forming:
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in this case a solution would form as there is more than enough energy for the solution to form from the heat of hydration the solution would likely not form because the energy required to break up the solute is greater than the energy given off by the formation of a solution
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solution would form but there would be no noticeable change in temperature Solution Equilibrium and Factors Affecting Solubility Similar to phase change, the dissolution of a solute in a solvent has three phases;
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once the rate of dissolution = the rate of recrystallization, a dynamic equilibrium has been reached once the dissolved solute is in a dynamic equilibrium with the solid solute (undissolved) then the solution is known as a saturated solution any additional solute to this saturated solution will not dissolve a solution containing less than the equilibrium amount of solute is an unsaturated solution -- if you add solute to an unsaturated solution it will dissolve under certain circumstances a supersaturated solution may form -- a solution containing more than the equilibrium amount of solute the solutions are unstable
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solute normally precipitates out of the solution Temperature Dependence of the Solubility of Solids solubility of solids can be highly dependent on temperature although exceptions exist the solubility of most solids in water increases with increasing temperature a common way to purify a solid is a technique known as recrystallization enough solid is added to water to create a saturated solution at an elevated temperature the solution cools and becomes supersaturated and the excess solid precipitates out of the solution if the solution cools slowly, the solid forms crystals as it comes out of the solution the crystalline structure tends to reject impurities, resulting in a purer solid Factors Affecting the Solubility of Gases in Water many solutions contain gas dissolved in a liquid; fish require the oxygen dissolved in the ocean to survive the affect of temperature the solubility of gases in liquids decreases with increasing temperature -- this is why gas evaporates out of water and begins to bubble as you heat water -- why you see bubbles when water boils
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Christopher Reinemann
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