CHAPTER 14 – SOLUTIONS1 Spontaneity of the Dissolution Process (The Dissolution Process) solute + solvent  solution25 mL H2O + 15 mL CH3CH2OH + 125 mL CH3COCH3  solution solute solute solvent*note that the solvent will always be in much higher concentration than the solute will be in the 7 homogeneous possibilities:solute solvent examplesolid liquid salt waterliquid liquid mixed drinksgas liquid carbonated drinksliquid solid dental amalgamssolid solid alloysgas solid metal pipesgas gas air (O, H, and N) the 2 heterogeneous possibilities:solute solvent examplesolid gas dust in the airliquid gas clouds and fog two major factors affect the dissolution of solutes:#1 -- enthalpy -- a measure of heat, Hsolutionwhere +H is exothermic (dissolution is favored) and -H is endothermic (dissolution is NOT favored)#2 -- entropy -- a measure of randomness/disorder, Smixingwhere +S is an increase in disorder (dissolution is favored) and -S is a decrease in disorder (dissolution is NOT favored)NaCl(s)  Na+(aq) + Cl-(aq)+S, increasing entropy (>0, favorable)Na+(aq) + Cl-(aq)  NaCl(s)-S, decreasing entropy (<0, notfav.)disorder almost always increases when mixing a solution (+S), so S is almost always > 0the ideal situation is:-H (exothermic), H < 0+S (more disordered), S > 0 solutes nearly always become more disordered upon dissolution the main factors that determine the heat of solution, Hsolution, are:solute-solute attractions -- things like ion-ion attraction, dipole-dipole attraction, etc.; overcoming solute-solute attractions requiresthe absorption of energy(+H, endothermic)Na+|Cl- + H2O …  breaking the bond between Na+ and Cl- in NaClsolvent-solvent attractions -- one example is hydrogen bonding in water; overcoming solvent-solvent attractions requires the absorption of energy(+H, endothermic)H2O - - | - - H2O  overcoming the attractive forces between the O’s and the H’sNaCl + H2O  +Hsolvent-solute attractions -- known as solvation; this releases energy(-H, exothermic)if the solvation energy is greater than the sum of the solute-solute and solvent-solvent attractions, then the dissolution is exothermic, -H or Hsolution < 0if the solvation energy is less than the sum of the solute-solute and solvent-solvent attractions, then the dissolution is endothermic, +H or Hsolution > 0so, Hsolution is a sum of the three processes described above, and dissolution is favored when the first two factors are small and the third factor is large!2 Dissolution of Solids in Liquids (The Dissolution Process) many solids that are very soluble in water are ionic crystal lattice energy -- the energy released (-H, exothermic) when 1.00 mol of formula units of a solid is formed from its constituent ions (molecules or atoms for non-ionic solids) in the gas phase; a measure of the attractive forces in a solidM+(g) + X-(g)  M+X-(s) + crystal lattice energycrystal lattice energy + M=X-(s)  M+(g) + X-(g)*note that if the first equation is an endothermic process, thenthe second equation is an exothermic process; also, if the firstequation is an exothermic process, then the second equation is an endothermic processcrystal lattice energy increases as charge density increases ()! in the picture below, the Li+ ion and the Cl- ion in the bottom right are hydrated ions energy of solvation or hydration energy (if the solvent is water) -- the energy released when solute particles are dissolved (when a solvent dissolves a solute) in an exothermic dissolution molar energy of hydration -- the amount of energy absorbed when 1.00 mol of formula units, in the form of gaseous ions, becomes hydratedMn+(g) + xH2O  [M(OH2)x]n+ + hydration energy for Mn+Xy-(g) + nH2O  [X(H2O)n]y- + hydration energy for Xy- hydration energy increases with increasing charge density ()!ion radius (Å)charge/radiusratioheat ofhydrationK+1.33 0.75 -351 kJ/molCa2+0.99 2.02 -1650 kJ/molCu2+0.72 2.78 -2160 kJ/molAl3+0.50 6.00 -4750 kJ/molnotice that the hydration energy increases as the charge density increasesremember the trend for ionic radii:K+  Ca2+  Al3+  N3-  O2-  F-  the “like dissolves like” rule says that polar molecules are soluble in polar solvents and that non-polar molecules are soluble in non-polar solvents London dispersion forces look like this:3 Dissolution of Liquids in Liquids (Miscibility) (The Dissolution Process) non-polar molecules essentially slide in between each other, fitting very close to one another; this close fit enhances London dispersion forces, which increases miscibilityfor example, CCl4 is very miscible in C6H6 (benzene)4 Dissolution of Gases in Liquids (The Dissolution Process) polar gases are more soluble in water than non-polar gasespolar gases are things like the strong acid gases -- HCl(g), HI(g), etc.HF(g) is also a polar gas (even though it is a weak acid) due to hydrogen bonding remember this particular polar gas formula:HI(g) + MHCO3 or MCO3  salt + H2O(l) + CO2(g)*note that H2CO3 is not included because it is very unstable polar gases can hydrogen bond with water some polar gases enhance their solubility by reacting with waterHBr(g) + H2O(l)  H3O+(aq) + Br-(aq)strong acidSO2(aq) + H2O(l)  H2SO3(aq)H2SO3(aq)  H3O+(aq) + HSO3-(aq)weak acid a few non-polar gases are soluble in water because they react with waterCO2(aq) + H2O(l)  H2CO3(aq)  H3O+(aq) + HCO3-(aq)very weak acid because gases have very weak solute-solute interactions, gases dissolvein liquids in exothermic processes5 Rates of Dissolution and Saturation (The Dissolution Process) finely divided solids dissolve more rapidly than large crystals due to an increase in surface area (the number of molecules of sugar exposed to water increase)compare the dissolution of granulated sugar and sugar cubes in coldwater: saturated solutions -- the maximum amount of solute that can be dissolved in a given volume of solventan equilibrium is established between dissolved and undissolved solutes; symbolically, this equilibrium is written as:MX(s)  M+(aq) + X-(aq)*note that in an equilibrium reaction, the forward rate of reaction is equal to the reverse rate of reactionexamples -- air that has 100% humidity and some solids dissolved inliquids supersaturated solutions -- have