Biology 2000 week of 2-1
Biology 2000 week of 2-1 200001
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This 3 page Class Notes was uploaded by Audrey Notetaker on Friday February 5, 2016. The Class Notes belongs to 200001 at Boston College taught by Danielle Taghian in Spring 2016. Since its upload, it has received 43 views. For similar materials see Molecules and Cells in Biology at Boston College.
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Date Created: 02/05/16
Chapter 11: Calculations with Unit Cells 2/1/16 Polymorphic – substance can exist in more than one structure Xray Diffraction crystallography: determine the structure; finds where each atom sits in 3D Crystals are highly ordered Constructive Interference: brighter, larger amplitude Destructive Interference: dimmer; smaller amplitude *If the difference in distance travelled by wavelength is an integer, then the waves are constructive so the light will be lighter Bragg’s Law: nλ=2dsinθ 2a n = integer (n = 1: first order diffraction; n = 2: second order diffraction, etc.) λ = wavelength (m) d = distance of separation between layers (m) θ = angle of incidence Chapter 12: Introduction to Solutions 2/3/16 Alloy: dissolving two metals Solution: homogeneous mixture (atoms, molecules, ions, solids, liquids, gas) Completely miscible liquids can be completely dissolved Solute: solid or gas dissolved; whichever is the smaller amount Solvent: liquid is dissolved *unreactive gases are completely miscible to each other Solubility: how much of a compound dissolves in a certain amount of solvent Like dissolves like (polar and polar / nonpolar and nonpolar) Group 1A, ammonium ions, and salts are soluble in water Unsaturated: more solute can be added and it will still dissolve Saturated: greater than or equal to the amount at which the solute will stop dissolving or it has completely dissolved Supersaturated: not in equilibrium; very unstable *things have a natural tendency towards disorder or entropy which leads to mixing Want the state of lowest energy o If solute/solvent forces are greater than the solute then there is no mixing o If solute/solvent forces are equal to the solute: solvent then there is mixing Molecular Solutions Gases: entropy predominates (is stronger) so there is mixing Non polar liquids: entropy is stronger so there is mixing Polar and non polar: entropy is weak because it takes too much energy to dissolve so there is no mixing *longer hydrocarbon chain becomes less polar and less likely to be miscible in water Solubility depends on: Iondipole force favors dissociation: bringing ions into solution Interactions of ions (lattice energy): favors order + Δ H is endothermic Needs/absorbs heat Cold Δ H is exothermic Releases heat Hot Dissolving a Solid 1. Break the crystal lattice – opposite of the lattice energy + Δ H 2. Break the hydrogen bonds (separate water) + Δ H 3. Mixing – ion dipole forces Δ H Chapter 12: Heat of Dissolution Concentration Terms 2/5/16 ΔH solution)=Δ H (solute+Δ H (solvent)+Δ H(mixing) ΔH solution)=Δ H (solute+Δ H(h ydration) *most ionic solids get more soluble the higher the temperature *most gases become less soluble as temperature increases *change in pressure has no effect on solubility of liquids or solids (because they are incompressible) in water but has a HUGE effect on gas Henry’s Law: S(gas) =K(h)P(gas) Solubility will change according to the temperature Coligative Property: only depends on quantity not quality; number of moles of whatever is added not what is actually added
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