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

Solutions Pure Solvent Pure Solute Mixture

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

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

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

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

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!

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+2 vs. Li+1 and K+1) The smaller the ion, the stronger the attraction (Li+1 vs. K+1)

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

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

MEASRUING Heat of Solution NH4(OH)2 The solution process is endothermic What is the Molar DHsoln ? Ba(OH)2 The solution process is exothermic What is the Molar DHsoln ?