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The boiling point of a substance is a measure of the amount of energy needed to:

Preview of Coming Attractions. The boiling point of a substance is a measure of the amount of energy needed to:.  increase the speed of the molecules in the liquid phase to that of their gas phase ( The heavier it is, the higher the boiling point).

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The boiling point of a substance is a measure of the amount of energy needed to:

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  1. Preview of Coming Attractions The boiling point of a substance is a measure of the amount of energy needed to:  increase the speed of the molecules in the liquid phase to that of their gas phase (The heavier it is, the higher the boiling point)  overcome any intermolecular forces (“molecular stickiness”)

  2. Substance Molar Mass Boiling Point (C) H2O 18 100 HF 20 20 H2S 34 -60 HCl 36 -85 SO2 64 -10 Water's Wick-ed Ways Consider the following polar molecules: Dipole moment 1.80 1.83 0.97 1.08 1.61 The polarity of a molecule is more important in determining boiling point than its mass.

  3. Water’s unusual properties are due to its: Surface tension: uneven distribution of the intermolecular dipole-dipole interactions increases the strength of the intermolecular hydrogen bonding at the surface Cohesive properties: a large molecular dipole moment causes water to stick to itself Adhesive properties: the small size and high polarity of water causes it to adhere (wet) other polar substances Non-polar polyester Polar spider silk (a polypeptide)

  4. How much will dissolve? Saturated solution: No more solute will dissolve. Unsaturated solution: Haven’t added enough solute to the solvent for the solution to be saturated. If more solute is added, it will dissolve. Supersaturated solution: Have ‘tricked’ the solution so that there is more solute dissolved in the solvent than is present in a saturated solution. Adding more solute causes the excess solute to precipitate out of solution.

  5. Solubility curves Plots the MAXIMUM number of grams of a solute that will dissolve in 100 g of the solvent at particular temperatures.

  6. 1. Is NaNO3 or KNO3 more soluble at 50o C? 2. Is a solution containing 80 g of NH4Cl at 80o C saturated, unsaturated or supersaturated?

  7. 3. What is least soluble at 40oC? Ce2(SO4)3 4. Is a solution containing 80 g of KNO3 at 80o C saturated, unsaturated or supersaturated? 5. At what temp. will crystals appear for the solution in #4? 50oC

  8. The Kinetic Theory of Matter Gas Gas The three common states of matter are: Indefinite volume Indefinite shape Definite volume Definite shape Definite volume Indefinite shape Liquid Liquid Gas

  9. The Kinetic Theory of Matter Three basic assumptions: 1. All matter is composed of small particles (atoms, molecules, ions). The amount of space (volume) that the particles take up depends upon the distance between the particles and not on the size of the particles themselves. 2. These particles are in constant random motion. 3. The particles undergo elastic collisions (no loss of energy) with each other and the walls of their container. Absolute zero: The temperature at which ALL molecular motion stops. (0 K = -273°C = -460°F)

  10. Solids: The particles in solids can be arranged in three different ways. 2. With a pattern that only repeats over short distances. • In a regular repeating pattern that extends over long distances. A crystalline material: Has long-range order A glassy material: Short-range order only

  11. Graphitic carbon: ‘glassy’ carbon Diamond: Crystalline carbon Charcoal: Amorphous carbon 3. Amorphous solids have no long or short range order. Allotropes: different structural forms of the same element

  12. H H O O Gas Liquid Intermolecular Forces: Whether a substance is a liquid, solid or gas depends upon the strength of the intermolecular forces holding it together. Solid Indefinite shape and volume Indefinite shape, definite volume Compressible Virtually incompressible Flows readily/rapid diffusion Flows readily/slow diffusion Let’s get to stickin’!! Definite shape and volume Virtually incompressible Does not flow Diffusion is very slow

  13. STRONGEST weakest Intermolecular Forces: the properties of materials (solubility, viscosity, boiling point, freezing point, heat capacity*) depend upon the strength of the interactions BETWEEN the particles. There are six types of intermolecular forces: • Ion-ion • Ion-dipole • H-bonding • Dipole-dipole • Dipole-induced dipole • Induced dipole-induced dipole (also called London Dispersion Forces, or LDF)

  14. Mg+2 O-2 Na+1 Cl-1 << 1. Ion-ion: exists between oppositely charged ions (atoms that have gained or lost electrons and are no longer electrically neutral). The strength of this interaction increases as the magnitude of the charge increases. NaCl is soluble in water, MgO is not. 2. Ion-dipole: exists between ions and polar molecules (e.g. water, alcohols)

  15. d+ d- No intermolecular H-bonding possible H-bonding between H on OH and O on next OH 3. H-bonding: Is a special case of dipole-dipole interaction because it is significantly stronger. It occurs wheneverH is bonded to either N, O or F. 4. Dipole-dipole: interaction between molecules with permanent dipoles that do not have H-bonding

  16. - + HCN 5. Dipole-induced dipole: The permanent dipole of a polar molecule causes a distortion of the electron cloud around a nonpolar molecule and INDUCES A TEMPORARY DIPOLE. C6H14 6. Induced dipole-induced dipole: A temporary redistribution of the electron cloud around a NONPOLAR molecule induces a temporary dipole in an adjacent NONPOLAR molecule. C6H14 C6H14

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