Chap 14 - 14 Solutions 1 The Dissolution Process Solutions...

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1 14 Solutions
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2 The Dissolution Process Solutions are homogeneous mixtures of two or more substances. Dissolving medium is called the solvent solvent . Dissolved species are called the solute solute .
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3 The Dissolution Process There are three states of matter (solid, liquid, and gas) which when mixed two at a time gives nine different kinds of mixtures. Seven of the possibilities can be homogeneous. Two of the possibilities must be heterogeneous.
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4 The Dissolution Process Seven Homogeneous Possibilities Solute Solvent Example Solid Liquid salt water Liquid Liquid mixed drinks Gas Liquid carbonated beverages Liquid Solid dental amalgams Solid Solid alloys Gas Solid metal pipes Gas Gas air
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5 The Dissolution Process Two Heterogeneous Possibilities Solute Solvent Example Solid Gas dust in air Liquid Gas clouds, fog
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6 Spontaneity of the Dissolution Process Consider the formation of a solution in which the solvent is a liquid. Two major factors affect dissolution of solutes: 1) enthalpy 2) entropy
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7 Spontaneity of the Dissolution Process 1. enthalpy - change of energy content of solution, Δ H solution If Δ H solution is exothermic (< 0) dissolution is favored. - Δ H If Δ H solution is endothermic (> 0) dissolution is not favored. + Δ H
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8 Spontaneity of the Dissolution Process 2. entropy - change in disorder, or randomness, of the solution Δ S mixing If entropy ( Δ S mixing ) increases (> 0) dissolution is favored. + Δ S If entropy ( Δ S mixing ) decreases (< 0) dissolution is not favored. - Δ S
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9 Spontaneity of the Dissolution Process Thus the best conditions for dissolution are: For the solution process to be exothermic (- Δ H). Δ H solution < 0 For the solution to become more disordered (+ Δ S). Δ S mixing > 0
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10 Spontaneity of the Dissolution Process Disorder almost always increases when mixing a solution, + Δ S. Δ S mixing is almost always > 0.
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11 Spontaneity of the Dissolution Process What factors affect Δ H solution (enthalpy or heat of a reaction)? There is competition between several different attractions. 1. Solute-solute attractions such as ion-ion attraction, dipole-dipole, etc. Overcoming solute-solute attractions require the absorption of energy.
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12 Spontaneity of the Dissolution Process 2. Solvent-solvent attractions such as hydrogen bonding in water. This also requires the absorption of energy to overcome.
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13 Spontaneity of the Dissolution Process 3. Solvent-solute attractions, solvation solvation , releases energy. If solvation energy is greater than the sum of the solute-solute and solvent-solvent attractions, the dissolution is exothermic, Δ H soln < 0 (- Δ H). If solvation energy is less than the sum of the solute-solute and solvent-solvent attractions, the dissolution is endothermic, Δ H soln > 0 (+ Δ H).
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14 Spontaneity of the Dissolution Process
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15 Dissolution of Solids in Liquids The energy released (exothermic) when a mole of formula units of a solid is formed from its constituent ions (molecules or atoms for nonionic solids) in the gas phase is called the crystal lattice crystal lattice energy energy .
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This note was uploaded on 09/18/2010 for the course CHEM 1212 taught by Professor Suggs during the Fall '08 term at UGA.

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Chap 14 - 14 Solutions 1 The Dissolution Process Solutions...

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