Liquids and Solids Chapter 10 Nov 15 9:56 AM Types of Solids Crystalline solids: Solids with highly regular arrangement of their components Amorphous solids: Solids with considerable disorder in their structures. Nov 15 1:29 PM 1
Types of Solids Lattice: A 3D system of points designating the positions of the components (atoms, ions or molecules) that make up the substance Unit Cell: The smallest repeating unit of the lattice structure. X Ray Diffraction: The method is to determine the structure of a crystalline solid. Diffraction patterns of light are measured and compared Nov 15 1:54 PM Types of Solids: Molecular solids Molecular Solids have discrete and relatively small molecules at the lattice points that are held together by IMFs Examples: ice, dry ice, and sugars. Properties: low melting/boiling points, poor conductors, low densities, typically soft. Nov 15 2:02 PM 2
Types of Solids: Ionic solids Ionic Solids have ions at the lattice points and held together by strong electrostatic attractions (stronger than traditional IMF's). Examples: Sodium chloride and lithium nitrate Properties Include: High melting/boiling points, brittle (due to cleavage), poor conductors as solids, good conductors as liquids or in solutions, high densities. Dec 2 8:44 AM Types of Solids: Network Solids Atomic/Molecular Network Solids: atoms/compounds at the lattice points and held together by directional covalent bonds (stronger than IMF and electrostatic) Examples: graphite, diamond, and quartz (SiO 2 ). Properties: high melting/boiling points, typically poor conductivity but it can vary, high densities, and typically hard Dec 2 8:44 AM 3
Types of Solids: Metallic Solids Metals are held together by nondirectional covalent bonds where the electrons are delocalized throughout the structure (weaker than directional covalent bonds) Closet Packing: A metallic crystal structure where the atoms are spherical and packed together and bonded to each other equally in all directions Properties: High melting/boiling points, good conductors, high densities, malleable/ductile. Nov 15 2:11 PM Types of Solids: Metallic Solids Alloy: A substance that contains a mixture of elements and has metallic properties Substitutional Alloy: Some of the host metal atoms are replaced by other metal atoms of similar size (Sterling Silver 93% silver 7% copper, Pewter 85% tin 7% copper 6% bismuth and 2% antimony) Interstitial Alloy: When some of the interstices (Holes) in the closet packed metal structure are occupied by small atoms (Steel contains carbon atoms in the holes of an iron crystal) Nov 15 2:25 PM 4
Liquids Properties: Low Compressibility (cannot be compressed) Lack of rigidity (ability to flow) (viscosity and surface tension) High Density (compared to gases) Nov 15 12:50 PM Liquids Vaporization (Evaporation): Molecules of a liquid escape the liquid's surface and form a gas Condensation: Vapor molecules reform a liquid Equilibrium: Two opposite processes exactly balanced with each other Vapor pressure: The pressure of the vapor present at equilibrium Nov 27 7:20 AM 5
Phase Change Heat Curve: A plot of temperature versus time for a process where energy is added at a constant rate L + G Gas S + L Liquid Solid Endothermic: Reactions require (take in) energy (heat) Exothermic: Reactions release (give off) energy (Heat) Breaking bonds is ALWAYS Endothermic Normal Melting Point: The temperature at which the solid and liquid states have the same vapor pressure under conditions where the total pressure is 1 atm Normal Boiling Point: The temperature at which the vapor pressure of the liquid is exactly 1 atm Nov 15 2:31 PM Phase Change Heat of vaporization (Enthalpy of vaporization): The energy required to vaporize 1 mole of a liquid at a pressure of 1 atm. Heat of Fusion (Enthalpy of fusion): The change in energy that occurs at the melting point when a solid melts Specific Heat Capacity: The energy required to raise the temperature of one gram of a substance by one degree Celsius q = (m)(c)δt q = energy (Joules or KJ) m = Mass (grams) C = Specific Heat Capacity ΔT = Change in temperature Nov 26 7:48 AM 6
Phase Change How many kilojoules are needed to raise the temperature of 112g of ice at 18.0 to steam at 109? C Ice = 2.087 J/g C Water = 4.184 J/g C Steam = 1.996 J/g ΔH Fus = 6.02 KJ/mol ΔH Vap = 40.7 KJ/mol Nov 15 2:31 PM Phase Change Phase Diagrams: A diagram that represents the phases of a substance as a function of temperature and pressure (This is in a CLOSED system) Triple Point: The point in which all states of matter exist Critical Point: The point where the critical pressure meets the critical temperature. After this point there is only a "intermediate fluid" that is neither vapor nor liquid Nov 28 3:58 PM 7
Phase Change Phase Diagram Fun Facts: A liquid boils at the temperature with the vapor pressure of the liquid equals the external pressure. This is why it takes longer to hard boil an egg in the mountains than it does at the ocean. Water will boil at a lower temperature where there is less pressure (mountains) meaning the egg has to cook longer to hard boil in the lower temperature. Nov 28 4:10 PM Chapter 11 8
Solution: Homogeneous mixture where a solute is dissolved in a solvent Dilute: Relatively little solute present Concentrated: Large amount of solute present Ways to Express Concentration: Molarity: Moles divided by Liters (Mol/L which is symbolized by M) Mass Percent (Weight Percent): The percent by mass of the solute in the solution Mole Fraction: The ratio of moles of a given component to the total number of moles Molality: Moles of solute per kilogram of solvent symbolized by a m 9
Steps of the Formation of a Liquid Solution 1). Separating the solute into its individual components (expanding the solute) 2). Over coming intermolecular forces in the solvent to make room for the solute (expanding the solvent) 3). Allowing the solute and solvent to interact to form the solution Think about the intermolecular forces!!! Steps 1 and 2 are commonly endothermic Step 3 is commonly exothermic 10
Enthalpy of Solution (ΔH soln ): The change in energy associated with the formation of the solution. It is the sum of the energy changes for all three steps. ΔH soln = ΔH 1 + ΔH 2 + ΔH 3 If ΔH has a positive sign the step was endothermic (energy absorbed) if ΔH has a negative sign the step was exothermic (energy was released) Enthalpy of Solution (ΔH soln ): ΔH soln = ΔH 1 + ΔH 2 + ΔH 3 Let's look at dissolving oil in water: Step 1: Expansion of the solute medium +ΔH Oil is a nonpolar substance that only has LDF holding it together. These intermolecular forces are weak and only require a small amount of energy to break apart, however since oil is a larger compound it will take more energy to "untangle" the molecules from each other Step 2: Expansion of the solvent large +ΔH Water has very strong intermolecular forces (Hydrogen bonds) that will require a lot of energy to separate the molecules. This will result in a large amount of energy Step 3: solute and solvent interaction The interaction between water (polar) and oil (nonpolar) will be negligible causing a very small release of energy small ΔH The medium and large positive step 1 and step 2 and the very small negative step 3, cause the overall process to be very large and positive. This means this solution will unlikely not occur. (Enthalpy is not the ONLY determining factor!!!) 11
Let's look at dissolving salt in water: Enthalpy of Hydration (ΔH hyd ): Combines the energy of step 2 and step 3 due to the fact that hydration is the process in which water separates from itself and surrounds the ions present in solution. NaCl(s) Na + (g) + Cl (g) ΔH 1 = 786 kj/mol H 2 O(l) + Na + (g) + Cl (g) Na + (aq) + Cl (aq) ΔH 2+3 (ΔH hyd ) = 783 kj/mol ΔH soln = 786 kj/mol 783 kj/mol = 3 kj/mol The overall reaction is positive, but it still occurs quite readily. This is due to the fact that enthalpy is not the only factor when determining whether a process will proceed readily. Entropy (chaos) is also taken into consideration. ΔH 1 ΔH 2 ΔH 3 ΔH soln Outcome Polar solute, Polar solvent Large Large Large neg Solution Forms Nonpoar solute, Polar solvent Nonpolar solute, nonpolar solvent Large Large Pos No Solution Solution Forms Polar solute, Non polar solvent Large Large Pos No Solution 12
Factors Affecting Solubility Structure Effect: Like dissolves like! Lets look at vitamin A vs. Vitamin C Factors Affecting Solubility Pressure effect: Pressure does not effect solids and liquids but does significantly effect gases. 13
Factors Affecting Solubility Nov 29 7:33 AM 14