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Chapter 12

Chapter 12 Study Guide

11 Pages
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Department
Chemistry
Course Code
CHMA11H3
Professor
Jamie Donaldson

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Chapter 12 Solutions
-solution is homogenous mixture
-solutions are mixtures in which atoms and molecules intermingle on the molecular and atomic
scale
-examples include ocean water, gasoline, and air
Thirsty Solutions: Why You Should Not Drink Seawater
-drinking seawater causes dehydration because seawater draws water out of body tissues
-draws water as it passes through stomach and intestine, resulting in diarrhea and further
dehydration
-seawater is a thirsty solution, one that draws more water to itself
-seawater is a solution, homogeneous mixture of two or more substances or components
-majority component is solvent
-minority component is solute
-in seawater, water is solvent and sodium chloride is main solute
-seawater draws water to itself due to nature’s tendency toward spontaneous mixing
-substances tend to combine into uniform mixtures, not separate into pure substances, unless it is
highly unfavourable energetically
-substances spontaneously mix together to form a more dilute solution of uniform concentration
-fluids in the body are more dilute than seawater
-nature’s tendency toward mixing (produce solutions of uniform concentration) and selective
permeability of cell membranes (allow water to flow in and out, but restrict flow of dissolved
solids) causes a flow of solvent out of the body’s cells and into seawater
-2solutions become more similar in concentration
-body fluid becomes more dilute and solution in the cell becomes more concentrated
-accumulation of extra fluid in intestines causes diarrhea
-decreased fluid in cells causes dehydration
Types of Solutions and Solubility
-solution can be composed of solid and liquid, gas and liquid, two liquids
-in aqueous solutions, water is solvent and solid/liquid/gas is solute
-sugar water and salt water are both aqueous solutions
-alcohol and carbon dioxide dissolves in water to form aqueous solution
-solubility is the amount of substances that will dissolve in a given amount of solvent
-solubility depends on nature’s tendency toward mixing and types of intermolecular forces
Nature’s Tendency toward Mixing: Entropy
-physical systems tend toward lower potential energy
-formation of solution does not necessarily lower potential of its constituent particles
-example is the formation of homogeneous mixture (solution) of 2 ideal gases
-at low pressure and moderate temperature, noble gas behaves as ideal gas
does not interact with each other in any way
www.notesolution.com
there are no significant forces between their constituent particles
potential energy remains unchanged when 2 noble gases mix
-mixing of two ideal gases does not lower potential energy
-tendency to mix is related to entropy
-entropy is measure of energy randomization/ energy dispersal in a system
-gas at temperature above zero K has kinetic energy due to motion of atoms
-gas and its kinetic energy become spread out or dispersed over larger volume
-mixture of 2 gases has greater energy dispersal, or greater entropy than the separated
components
-2 ideal gases mix due to the pervasive tendency for energy to spread out or disperse, whenever it
is not restrained from doing so
-example of tendency toward energy dispersal is the transfer of thermal energy from hot to cold
places
-thermal energy at one will spontaneously spread along the entire body of object
-kinetic energy becomes dispersed over large volume because particles become dispersed
-tendency of energy to disperse is why thermal energy flows from hot to cold place, and not the
other way around
-energy does not spontaneously concentrate itself so one end is not hot and the other end is cold
does not take place
The Effect of Intermolecular Forces
-when intermolecular forces are absent, 2 substances spontaneously mix to form a homogeneous
solution
-intermolecular forces exist between
1) solvent and solute particles
2) solvent and solvent particles
3) solute and solute particles
Relative Interaction and Solution Formation
Solvent-solute interaction > solvent-solvent &
solute-solute interactions
Solution forms
Solvent-solute interaction = solvent-solvent &
solute-solute interactions
Solution forms
Solvent-solute interaction < solvent-solvent &
solute-solute interactions
Solution may or may not form, depending on
relative disparity
-miscible is when 2 substances are soluble in each other in all proportions due to similar
magnitude in all three interactions
-formation of solution is due to tendency toward mixing/ toward greater entropy
-if disparity is small, tendency to mix result, solution forms even though the process is
energetically uphill
-if disparity is large, solution will not form
www.notesolution.com
-energy require to pull water molecules away from one another is too great and too little energy
is returned from the interaction with solute molecules
-solution does not form when mixing non-polar molecules with water
-tendency to mix is strong, but it cannot overcome large energy disparity between strong solvent-
solvent interactions and weak solvent-solute interactions
-like dissolves like to predict formation of solutions
Energetics of Solution Formation
-energy changes in solution formation
1) Separation of solute into constituent particles
-always endothermic (positive H) because energy is required to overcome forces that hold
solute together
-Hsolute > 0
2) Separation of solvent particles from each other to make room for solute particles
-also endothermic because energy is required to overcome intermolecular forces among solvent
particles
-Hsolvent > 0
3) Mixing of solute particles with solvent particles
-exothermic because energy is released as solute particles interaction (through intermolecular
forces) with solvent particles
-Hesss law, overall enthalpy change in solution is enthalpy of solution (Hxoln)
Hsoln = Hsolute + Hsolvent + Hmix
Endo (+) endo (+) exo (-)
1) Hsoln = 0
-increasing entropy upon mixing drives formation of solution
-overall energy of the system remains nearly constant
2) Hsoln = negative
-solution process is exothermic
-tendency toward lower energy and tendency toward greater entropy drive formation of solution
3) Hsoln = positive
-solution process is endothermic
-if H is not too large, tendency toward greater entropy will still drive formation of solution
-if Hsoln is too large, solution will not form
Aqueous Solution and Heat of Hydration
-heat of hydration is the sum of Hsolvent and Hmix
-enthalpy change that occurs when 1 mol of gaseous solute ions are dissolved in water
-due to ion-dipole interaction that occur between dissolved ion and water molecules
-ion-dipole interaction is much stronger than hydrogen bond
www.notesolution.com

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Description
Chapter 12 Solutions -solution is homogenous mixture -solutions are mixtures in which atoms and molecules intermingle on the molecular and atomic scale -examples include ocean water, gasoline, and air Thirsty Solutions: Why You Should Not Drink Seawater -drinking seawater causes dehydration because seawater draws water out of body tissues -draws water as it passes through stomach and intestine, resulting in diarrhea and further dehydration -seawater is a thirsty solution, one that draws more water to itself -seawater is a solution, homogeneous mixture of two or more substances or components -majority component is solvent -minority component is solute -in seawater, water is solvent and sodium chloride is main solute -seawater draws water to itself due to natures tendency toward spontaneous mixing -substances tend to combine into uniform mixtures, not separate into pure substances, unless it is highly unfavourable energetically -substances spontaneously mix together to form a more dilute solution of uniform concentration -fluids in the body are more dilute than seawater -natures tendency toward mixing (produce solutions of uniform concentration) and selective permeability of cell membranes (allow water to flow in and out, but restrict flow of dissolved solids) causes a flow of solvent out of the bodys cells and into seawater -2solutions become more similar in concentration -body fluid becomes more dilute and solution in the cell becomes more concentrated -accumulation of extra fluid in intestines causes diarrhea -decreased fluid in cells causes dehydration Types of Solutions and Solubility -solution can be composed of solid and liquid, gas and liquid, two liquids -in aqueous solutions, water is solvent and solidliquidgas is solute -sugar water and salt water are both aqueous solutions -alcohol and carbon dioxide dissolves in water to form aqueous solution -solubility is the amount of substances that will dissolve in a given amount of solvent -solubility depends on natures tendency toward mixing and types of intermolecular forces Natures Tendency toward Mixing: Entropy -physical systems tend toward lower potential energy -formation of solution does not necessarily lower potential of its constituent particles -example is the formation of homogeneous mixture (solution) of 2 ideal gases -at low pressure and moderate temperature, noble gas behaves as ideal gas does not interact with each other in any way www.notesolution.comthere are no significant forces between their constituent particles potential energy remains unchanged when 2 noble gases mix -mixing of two ideal gases does not lower potential energy -tendency to mix is related to entropy -entropy is measure of energy randomization energy dispersal in a system -gas at temperature above zero K has kinetic energy due to motion of atoms -gas and its kinetic energy become spread out or dispersed over larger volume -mixture of 2 gases has greater energy dispersal, or greater entropy than the separated components -2 ideal gases mix due to the pervasive tendency for energy to spread out or disperse, whenever it is not restrained from doing so -example of tendency toward energy dispersal is the transfer of thermal energy from hot to cold places -thermal energy at one will spontaneously spread along the entire body of object -kinetic energy becomes dispersed over large volume because particles become dispersed -tendency of energy to disperse is why thermal energy flows from hot to cold place, and not the other way around -energy does not spontaneously concentrate itself so one end is not hot and the other end is cold does not take place The Effect of Intermolecular Forces -when intermolecular forces are absent, 2 substances spontaneously mix to form a homogeneous solution -intermolecular forces exist between 1) solvent and solute particles 2) solvent and solvent particles 3) solute and solute particles Relative Interaction and Solution Formation Solvent-solute interaction > solvent-solvent & Solution forms solute-solute interactions Solvent-solute interaction = solvent-solvent & Solution forms solute-solute interactions Solvent-solute interaction < solvent-solvent & Solution may or may not form, depending on solute-solute interactions relative disparity -miscible is when 2 substances are soluble in each other in all proportions due to similar magnitude in all three interactions -formation of solution is due to tendency toward mixing toward greater entropy -if disparity is small, tendency to mix result, solution forms even though the process is energetically uphill -if disparity is large, solution will not form www.notesolution.com
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