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EXOTHERMIC

EXOTHERMIC. ENDOTHERMIC. Why upon mixing do some solutions get cold while other release heat?. Heat of Solution: D H soln. The amount of heat involved in the process of solution formation. Net energy ( D H soln ) is the sum of the parts. 2. Hydrate ions. 1. Break ions apart.

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EXOTHERMIC

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  1. EXOTHERMIC ENDOTHERMIC Why upon mixing do some solutions get cold while other release heat?

  2. Heat of Solution: DHsoln The amount of heat involved in the process of solution formation

  3. Net energy (DHsoln) is the sum of the parts 2. Hydrate ions 1. Break ions apart DHsoln = 1in + 2out = 821 – 819 = 2 kJ/mol

  4. Neg. = out (h T) Positive = in (,T) DHsoln = DHs + DHaq

  5. Heat of Solution If the enthalpy of formation of the solution is more negative that that of the solvent and solute, the enthalpy of solution is negative. The solution process is exothermic!

  6. Energy of a System Depends on the polarity of the solvating molecule, size of the ions and the charge The higher the charge, the stronger the attraction (Mg+2vs. Li+1 and K+1) The smaller the ion, the stronger the attraction (Li+1 vs. K+1)

  7. Heat of Solution: DHsoln Determines the solubility of a substance: If the DHsoln is very positive, water does not have enough energy to break ions apart and it will NOT dissolve If the DHsoln is negative, water will gain energy from ions and it will dissolve

  8. Hydration Energy 1. Explain why the enthalpy of hydration of Na+ is more negative than that of Cs+. Na+ is smaller size 2. Explain why the enthalpy of hydration of Mg2+ is more negative than that of Cs+. Mg2+has greater charge 3. Which should have a more negative enthalpy of hydration F-or Cl- ? Explain F- is smaller size

  9. Solutions Pure Solvent Pure Solute Mixture

  10. When copper chloride is dissolved in water, the ions are cloaked in water molecules Solvation

  11. Definitions Solutions can be classified as saturated or unsaturated. A saturated solution contains the maximum quantity of solute that dissolves at that temperature.

  12. Solubility: Maximum amount of solute per 100 g solvent SATURATED SOLUTIONS UNSATURATED SOLUTIONS

  13. Dissolving Effects: c34 • Saturated Solution- maximum amount of solute in solution • Any extra solute added just sits on bottom. • Unsaturated- less than max. solute than then can be dissolve. • Supersaturated- A solution containing more solute than normal for a given temperature. • Must heat a saturated solution up. Then return it to room temperature.

  14. For a Supersaturated solution, when more solute is added, the extra solute will settle to the bottom

  15. Supersaturated Sodium Acetate • One application of a supersaturated solution is the sodium acetate “heat pack.” • Sodium acetate has an ENDOthermic heat of solution.

  16. Temperature effects the solubility of a substance

  17. Solubility Curves How much LiCl will dissolve into 100 ml of water at a temperature of 20 C? How much KCl will dissolve into 500 ml of water at a temperature of 80 C? How much RbCl will fall out of solution if 200 ml of solution is cooled from a temperature of 80 C to 20 C?

  18. Dissolving Effects • Solubility- the quantity of solute that will dissolve in 100 g of solvent at a set temperature • If solution is holding the MAX. Amount of solute called saturated • Solidionic compounds: more in with higher temperature • Gases: More in at lower temperatures

  19. Dissolving Gases & Pressure Gas solubility can be changed by both the temperature and PRESSURE. When the can of soda is opened the pressure (Pgas) drops and causes the solubility to decrease.

  20. Henry’s Law Gas solubility (mol/L) = Sg Sg = kH • Pgas kH = Henry’s law constants for O2 = 1.66 x 10-6 M/mmHg When Pgas increases, solubility increases.

  21. Henry’s Law What is the concentration of oxygen in fresh water when the air pressure is 1 atm? Sg = kH • Pgas kHfor O2 = 1.66 x 10-6 M/mmHg O2 = 21% so 0.21(760 torr) = Pgas Sg= 1.66 x 10-6 M/mmHg • 160 torr = 2.66 x 10-4 M What is the concentration of oxygen in milligrams/ liter? O2 = 8.5 mg/L

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