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SOLUTIONS
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1 How they Form Mr. Shields Regents Chemistry U12 L04
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SOLUTIONS. How they Form. Mr. ShieldsRegents Chemistry U12 L04. The Solution Process. We’ve mentioned earlier that there are various kinds Of Soln’s but we’re only going to focus on a few … 1) Solids in liquid 2) Gas in liquid - ionic solids CO 2 , O 2 etc - PowerPoint PPT Presentation
Transcript of SOLUTIONS
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How they Form
Mr. Shields Regents Chemistry U12 L04
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The Solution ProcessThe Solution ProcessWe’ve mentioned earlier that there are various kindsOf Soln’s but we’re only going to focus on a few …
1) Solids in liquid 2) Gas in liquid - ionic solids CO2, O2 etc - molecular solids
3) Liquid in Liquid- Polar liquids- Non-polar liquidsLet’s start by looking at how an ionic solid dissolvesIn a Polar liquid like water
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Dissolving SolidsDissolving SolidsLet’s look at how an ionic compound like NaCl dissolves in water. Recall …
- NaCl is ionic and exists as a crystal lattice- It contains both + & - ions
-And secondly Water is a polar molecular liquid- It has both a + & - end
-
+
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DissolvingDissolvingWhen a crystal of NaCl is dropped into water itStarts to dissolve. So what’s this mean?
This means thearranged orderOf the Crystal latticeBreaks downAnd itBecomes …A homogeneousmixture of Ions in sol’n
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DissolvingDissolvingBut how does the process of dissolving actually happen?
Polar water alignsitself to the + and– ions at thesurface of theNaCl crystallattice.
This is a form ofIntermolecularAttraction betweenmolecules. Note thathere it is a force between different molecules.
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DissolvingDissolvingThe force of attraction between the solute and the solvent are Sufficient to overcome the force of attraction between thePositive and negative ions (Na+ and Cl-) in the crystal lattice .
Once the water overcomes the force of the attraction ofThe ions in the crystal theseparated ions are surroundedBy the water molecules.
This process is known asSOLVATION. If theSolvent is water it isCalled HYDRATION.
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Solvation (Hydration)Solvation (Hydration)
Na+- + +
- + +
- + + -
+
+
Cl-
- + +
- + +
- +
+ -
+ +
Na+- + +
- + +-
+ + - +
+
Cl-
- + +
- + +
- +
+ -
+ +
H20Of Hydration
Solvated (Hydrated) Ion
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Energy Balance of Solvation Energy Balance of Solvation This whole process of dissolving involves 3 energy steps:
1) Breaking of attraction between solvent particles
- Requires energy to be absorbed
(it’s endothermic)
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Energy Balance of Solvation Energy Balance of Solvation
2) Breaking of attraction between solute particles- requires energy (also endothermic)
3) Attraction between solute and solvent
- Results in the release of energy
(an exothermic process)
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The Heat of SolutionThe Heat of SolutionThe Total Energy (heat) absorbed or released duringsolvation is known as the HEAT OF SOLUTION (Hsol)
If the heat of Sol’n (Hsol) is positiveThe solution process is endothermic+Hsol = endothermic process
If the heat of Sol’n is negativeThe solution process is exothermic-Hsol = exothermic process
HHsolsol = H = Hstep1step1 + H + Hstep2step2 + H + Hstep3step3 (+) (+) (-)
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Energy Balance of SolavationEnergy Balance of Solavation Whether the overall solvation process will be endothermic or exothermic depends on the Energies involved is steps 1, 2, and 3.
When some compounds are dissolved in waterThe sol’n turns colder
-This is the more common result
Certain other compounds when dissolvedin water will turn the solution warmer
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Heat of Solution Examples Heat of Solution Examples Solutes that are exothermic upon dissolving(i.e sol’n gets hotter):
CaCl2 + H2O exothermic solvation process (-82.8 KJ/mol)
NaOH + H20 exothermic solvation process (-44.2 KJ/mol)
Solutes that are endothermic upon dissolving(i.e sol’n gets colder):
NH4NO3 +H2O endothermic solvation process (+25.4 KJ/mol)
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Practical use ProblemPractical use ProblemCaCl2 is used in a solvation process to help melt iceOn roads and sidewalks (i.e. the solution gets hot).
NH4NO3 is used in Cold Packs and Na2S2O3 is used in Heat packs. What is H for each (is it positive or negative)?
CaCl2 + H20 Negative Heat of Solution (-Hsol)NH4NO3 + H20 Positive Heat of Solution (+Hsol)Na2S2O3 + H20 Negative Heat of Solution (-Hsol)
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Table ITable I Open your reference tables to Table IOpen your reference tables to Table I
What is the HWhat is the Hsolsol of KNO of KNO33??+34.89+34.89
What is the HWhat is the Hsolsol of LiBr? of LiBr?-48.83-48.83
Which one when dissolved in water will Which one when dissolved in water will decreasedecrease the temperature of the solution?the temperature of the solution?
KNO3 / Hsol is Positive / Hsol is EndothermicKNO3 / Hsol is Positive / Hsol is Endothermic
