Chapter 12 CHEM 1200
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Popular in Chemistry
This 5 page Class Notes was uploaded by Alexi Martin on Monday February 22, 2016. The Class Notes belongs to CHEM 1200 at Rensselaer Polytechnic Institute taught by Dr. Alexander Ma in Spring 2016. Since its upload, it has received 66 views. For similar materials see Chemistry II in Chemistry at Rensselaer Polytechnic Institute.
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Date Created: 02/22/16
Chapter 12 Liquids Three phases of water densities of ice and liquid water, an increased density of water vapr liquid water is denser then ice Degrees of Freedom particles have 1/more types of freedom of motion translational:one position to another, gas rotationalreorient direction, liquid, gas vibrational oscillate about a point liquid gas and solid Solids packed and fixed vibrate incompressible retain shape and volume in a new container, cannot flow crystalline solidsorderly geometric patterns (salt and diamonds) amorphous solids: no patterns over a long range (plastic and glass *melting and boiling point at a single temperature are 1st order transitions* Liquids closely packed but can move incompressible assume volume of a container, do not expand/escape from each other ~first order reactionsmelting/freezing, boiling/condensing, deposition/sublimation~ ~making glass 2nd order transition~ Liquid crystal mesophase 1st order transition 2 types rod like or disc like carbonaceous mesophase= tar Gases free movement translational constantly moving can be compressed will fill a container’s shape Kinetic Molecular Theory state depends on 1. amount or # of particles 2. strength of attraction between particles, ex gases have complete freedom, they can overcome attractive forces, solids are locked in place, not enough KE, liquids have limited energy, they can overcome KE a bit however their particles are still attached 3. an increase of energy yields an increase in motion, the more motion the more freedom they have KEavg= 3/2RT=3/2KT f or 1 mol Attractive forces 1 electrostatic strength varies, depends on kinds of particles, the stronger the forces the more they will be stationary no material lacks particle motion abs S is positive KE of Gases increases it overcomes attraction it will be a gas an ideal gas=ideal freedom large spaces between particles low densities and will be compressionable KE of Solids attractive strong forces w/o any motion (vibrational only) KE of Liquids partially overcome, limited notion ▯G=0 @ transition temperature Phase Changes attractive forces are fixed, change requires changing KE solids melt because KE overcomes almost all forces Gases condensed lower temperature or at higher pressure phase changes are 1st order transitions Intermolecular attractions strength determines state moderate to strong liquid or solid, weak=gas stronger forces yields higher boiling point or a higher melting point Attractions? attractive forces + ion ion polar polar (Hydrogen bonding) nonpolar will temperature changes E= (1/4πE0)(q1q2/r^2) Coulomb's Law larger charge=stronger attraction smaller in comparison to bonding, larger distances Trends in attraction stronger larger E separate particles (list below increasingly stronger) dispersion temporary polarity in molecules unequal e distribution dipoledipole permanent polarity in molecular structures hydrogen bonding H attracted to extremely electronegative atoms ion dipole + ions surrounded by water example NaCl (aq) Dispersion (weakest force) fluctuations of a temporary dipole, caused by excess e density and depeleted e density also called London Forces size polarizability (large electron cloud) shape of the moleculesize all atoms have them only last for a period of time DipoleDipole (weaker force) polar permanent dipole 2 bond polarity and shape dipole moment always remains in induced dipole adds to attractive forces example 1: CH2Cl electronegative forces H=2.1 C=2.5 Cl=3 dipoledipole? if you draw the structure it has a tetrahedral shape and it is cis 2.00.es 5 y Hydrogen Bonding stronger force) electronegative OH NH H+ e pulled away and deshielded from + to Increase in boiling point and melting point account for 2 to 5% of covalent bonds Attractive Forces and Solubility Like dissolves like Immiscible liquids will see different layers Ion Dipole attractio strongest force) ions attracted to dipole of polar molecule ion dipole attraction determines solubility example 2: H3OH polar hydrogen bonding and CH3Cl are polar Surface Tension tendency to minimize surface area layer on the surface behaves differently than the interior can cause something denser than water to float surface molecules are less stable Factors Affecting Surface Tension High temperature and low ST, the stronger the intermolecular forces higher ST Viscosity larger intermolecular attractions higher volume 1 noise=1 P=1 g/cm*s > cP H2O= 1cP measuring viscosity: spindle, rotational, capillary factors affecting V> stronger intermolecular forces, more resistance, more spherical shaped molecule lower V Higher temperature, lower viscosity Capillary Action ability of liquid to flow up within a tube against gravity cohesivehold liquid molecules together adhesive attract out liquid molecule to tube narrower the tube the higher the liquid will travel convex Hg (metallic bonding) cohesion is greater than adhesion Meniscus concave down cohesion lower than adhesion Distribution of KE constantly in motion (solid, liquid or gas) Kavg is proportional to T some have more, some have less, some have average 3 Vaporization ndothermic fast evaporation= volatile larger the surface area, the faster the rate of evaporation (becoming a gas increase in vapor pressure Condensation exothermic loosing E through collisions gas becomes a liquid and forms droplets on objects Heat of Vaporization ▯Hcondensation= ▯Hvaporization example 3: 155x 1 mol/40.7 kJx18.02g/1mol = 68.6 g H2O 90.0 gx1mol/60.09x39.9/1mol= 59.8 kJ Dynamic Equilibrium rate V=C, they will occur at the same rate Vapor Pressure pressure exerted by water, weaker attractive forces= more molecules, weaker attractive forces greater vapor pressure, the greater the vapor pressure the more volatile the liquid Dynamic Equilibrium greater the volume the smaller the vapor pressure, vapor amount increases until it reaches a new equilibrium Vapor Pressure vs Temperature higher the temperature the greater number of molecules the greater the vapor pressure Boiling Vapor pressure=external pressure Heating Curve of a liquid q=mC▯T on the curved portions of the graph use the above equation width of the flat portions of the graph is the magnitude of ▯H vaporization, the greater the specific heat the greater the slope on the flat portions of the graph use the below equation n▯Hvaporization ClausiusClapeyron Equations: 1. ln (Pvap)=(▯vap/R)(1/T)+ln(ß) 2. ln (P2/P1)= (▯Hvap/R)(1/T21/T1) example 4: ln (p2/760)= .0352/8.314(1/(64.6+273)1/12+273) = 75.4 torr ln(P2/760)= 0.0407/8.314(1/2981/377)=2 8 torr Supercritical Fluid liquid is heated in a sealed container, vapor collects, pressure increases, density and volume increases, density of the liquid decreases the meniscus disappears and forms a supercritical fluid properties of a gas and liquid The Critical Point required to produce supercritical fluid at a supercritical temperature critical pressure= critical temperature 4 increase in temperature, C temperature, gas cannot condense to a liquid no matter how high the pressure Sublimation and Deposition vibrate, surface may become a gas= sublimation deposition a gas become a solid both can exist equally at dynamic equilibrium, Temperature decreases melting point solids can have a vapor pressure solid to gas ▯H increases ▯S increases, gas to a solid ▯H decreases and ▯S decreases Melting=Fusion solid heats up until the molecules vibrate more temperature reaches melting point, energy to overcome attractions to melt the solid opposite is freezing Heating Curve of a solid linearity q=mC▯T temperature @ melting point, heat melting the solid yields a constant temperature solid to a liquid is an increase in temperature ice/water temperature 0 at 1 atm Energetics of Melting increase in energy lost, decrease in kinetic energy melting is endothermic ▯H>0, freezing ▯H<0 Melting, energy needs to overcome attractions ▯S>0 because there is more disorder Heat of Fusion always endothermic ▯H + temperature dependant ▯H crystal= ▯H fusion less than ▯Hvap because a lot more intermolecular forces are required to break to become a gas ▯Hsub=▯Hfus+▯Hvap example 5: segment 1 q=mC▯T 18(2.09)(25)= 0.941 kJ segment 2: n▯Hvap= 1(6.02)=6.02 kJ segment 3 (same equation as 1)= 18(4.18)100=7.52 segment 4: (same equation as 2) 1(40.7)= 40.7 segment 5: (same as 1) 25(18)2.01=0.904 kJ add all of them together 5 6.1 kJ 5
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