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Types of Bonding in Crystalline Solids. Physical Properties of Solutions Chapter 13.

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Presentation on theme: "Types of Bonding in Crystalline Solids. Physical Properties of Solutions Chapter 13."— Presentation transcript:

1 Types of Bonding in Crystalline Solids

2 Physical Properties of Solutions Chapter 13

3 Solution - a homogenous mixture of 2 or more substances Solute - the substance(s) present in the smaller amount(s) Solvent - the substance present in the larger amount Table 13.1

4 Solutions The intermolecular forces between solute and solvent particles must be strong enough to compete with those between solute particles and those between solvent particles. “Like dissolves like”

5 Solutions How Does a Solution Form? As a solution forms, the solvent pulls solute particles apart and surrounds, or solvates, them. The Effect of Intermolecular forces Fig 13.1 Dissolution of an ionic solid inwater

6 Solutions Fig 13.2 Hydrated Na + and Cl − ions The negative end of the water dipoles point toward the positive ion Positive ends point toward the negative ion Result is hydrated ions

7 Three types of interactions in the solution process: solute-solute interaction solvent-solvent interaction solvent-solute interaction  H soln =  H 1 +  H 2 +  H 3 Fig 13.2 ΔH1ΔH1 ΔH2ΔH2 ΔH3ΔH3

8 Solutions Energy Changes in Solution Formation The enthalpy change of the overall process depends on  H for each of these steps. Fig 13.4 Enthalpy changes accompanying solution processes

9 Solutions Solution Formation, Spontaneity, and Entropy Enthalpy is only part of the picture Increasing the disorder or randomness of a system tends to lower the energy of the system Entropy ≡ degree of randomness or disorder in a system Solutions favored by increase in entropy that accompanies mixing Fig 13.6

10 Solutions Dissolution is a physical change — you can get back the original solute by evaporating the solvent If you can’t, the substance didn’t dissolve, it reacted: Caveat Emptor! Just because a substance disappears when it comes in contact with a solvent, it doesn’t mean the substance dissolved. Fig 13.7

11 Solutions Unsaturated solution - contains less solute than the solvent has the capacity to dissolve at a specific temperature Supersaturated solution - contains more solute than is present in a saturated solution at a specific temperature Sodium acetate crystals rapidly form when a seed crystal is added to a supersaturated solution of sodium acetate. Saturated solution - contains the maximum amount of a solute that will dissolve in a given solvent at a specific temperature Fig 13.10

12 “like dissolves like” Two substances with similar intermolecular forces are likely to be soluble in each other: non-polar molecules are soluble in non-polar solvents CCl 4 in C 6 H 6 polar molecules are soluble in polar solvents C 2 H 5 OH in H 2 O ionic compounds are more soluble in polar solvents NaCl in H 2 O or NH 3 (l) Factors Affecting Solubility

13 Solutions Factors Affecting Solubility Acetone is miscible in water H2OH2O C 6 H 14 Hexane is immiscible in water can hydrogen bond with water

14 Solutions Factors Affecting Solubility Fig 13.12 Structure and solubility Glucose (which has hydrogen bonding) is very soluble in water Cyclohexane has no polar OH groups and is insoluble in water

15 Solutions F ACTORS A FFECTING S OLUBILITY The more similar the intermolecular attractions, the more likely one substance is to be soluble in another: Fat-solubleWater-soluble Fig 13.13

16 Solutions  Solubility of liquids and solids does not change appreciably with pressure  Solubility of a gas in a liquid is directly proportional to its pressure Fig 13.14 Effect of pressure on gas solubility

17 S g = kP g where S g ≡ solubility of the gas k ≡ the Henry’s Law constant for that gas in that solvent P g ≡ partial pressure of the gas above the liquid Fig 13.15 Solubility decreases as pressure decreases Pressure Effect on Gases in Solution Henry’s Law:

18 Temperature Effect on Solids and Liquids Generally, the solubility of solid solutes in liquid solvents increases with increasing temperature Fig 13.17 Solubilities of several ion compounds as a function of temperature

19 Temperature Effect on Gases Fig 13.18 Variation of gas solubility with temperature The opposite is true of gases: Carbonated soft drinks are more “bubbly” if stored in the refrigerator Warm lakes have less O 2 dissolved in them than cool lakes

20 8/21/86 CO 2 Cloud Released 1700 Casualties Lake Nyos, West Africa Earthquake? Landslide? Wind/Rain?

21 Chemistry In Action: The Killer Lake Lake Nyos, West Africa

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