CHMA11H3 Lecture Notes - Molar Concentration, Mole Fraction, Colloid

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16 Feb 2011
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12.1 Thirsty Solutions: Why You Should Not Drink Seawater
Solution: a homogenous mixture of two or more substances or components
Solvent: majority component (water)
Solute: minority component
Seawater is a thirsty solution b/c of its tendency to MIX
12.2 Types of Solutions and Solubility
Aqueous solution: water is the solvent and solid, liquid or gas is the solute
Solubility of a substance is the amount of substance that will dissolve in a given
amount of solvent
Natures Tendency toward Mixing: Entropy
Formation of solution doesnt necessarily mean lower the potential energy of the
particles
Homogeneous mixture mixture of two ideal gases
Neon and argon behave as ideal gases at low pressure and moderate temperature
Two gases mix b/c of entropy but not because of lowering potential energy
(remains unchanged)
Entropy: a measure of energy randomization or energy dispersal in a system
Ex. Neon and argon gas both has kinetic energy confined in a system with
any temp. above 0K, when gases mix, Ek spreads out/dispersed over a larger
volume therefore mixture of gases has greater energy dispersal/greater
entropy
The pervasive tendency for energy to spread out, or disperse, whenever it is not
restrained from doing so is the reason that two ideal gases mix.
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Thermal energy from hot to god is another tendency toward energy dispersal
The Effect of Intermolecular Forces
Intermolecular forces exists between: solvent-solute, solvent, and solute particles
Solvent-solute
interaction >Solvent-solvent +
solute-solute
interaction
Solution forms
Solvent-solute
interaction =Solvent-solvent +
solute-solute
interactions
Solution forms
Solvent-solute
interaction <Solvent-solvent +
solute-solute
interaction
Solution may/may
not form, depending
on relative disparity
Miscible: the ability of two or more substances to be soluble in each other in all
proportions
Formation of solution is b/c of tendency of mixing/greater entropy
Disparity large solution will not form
Ex. H2O has strong H-bonding attraction but cannot form hydrogen bond w/
hexane
Energy to pull H2O molecules is too great and too little energy is retuned
when the water molecule interacts with hexane therefore solution is not
formed
like dissolves like
12.3 Energetic of Solution Formation
Understand energy changes associated w/ solution formation by:
1.Separating solute into its constituent particles
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2.separating the solvent particles from each other to make room for solute
particles
3.Mixing solute particles with the solvent particles
Enthalpy of solution: the overall enthalpy change upon solution formation
H(solution) = H (solute endo +) + H(solvent endo +) + H(mix exo - )
Endothermic terms = magnitude to exothermic Hsolution = 0
Endothermic terms < magnitude to exothermic Hsolution = exothermic
Endothermic terms > magnitude to exothermic Hsolution = endothermic
Aqueous Solutions and Heats of Hydration
Heat of hydration: the enthalpy change that occurs when 1 mol of the gaseous
solute ions are dissolved in water
1.Hsolute < Hhydration
Exothermic
Feels warm
(-)
2.Hsolute > Hhydration
Endothermic
Feels cold
(+)
3.Hsolute = Hhydration
Solute dissolve in water solution do not undergo noticeable change
in temperature
12.4 Solution Equilibrium and Factors Affecting Solubility
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