Lecture 26 Liquids 1 phase changes heat capacity Read HW BLB 5 5 11 4 BLB 5 48 49 51 11 33 37 39 Know viscosity surface tension cohesive adhesive forces phase changes heat capacity calorimetry Need help Get help TAs in CRC 211 Whitmore and SI hours on Chem 110 website my office hours Mon 12 30 2 Tues 10 30 12 in 324 Chem Bldg or 326 Chem Bonus deadline for BST 8 Intermolecular forces March 26 Bonus deadline for BST 9 Solutions dilutions April 2 Exam 3 Monday April 6 6 30 Check out the grade u lator http courses chem psu edu chem110 spring grade htm Sheets Page 1 Lecture 26 Manifestations of IM forces cohesive forces forces between molecules for example viscosity resistance to flow surface tension E needed to increase vapor pressure more next time BP MP Hvap Hsub adhesive forces forces between a the surface for example water glass interactions water oil interactions meniscus formation capillary action glue non stick surfaces Sheets Page 2 Lecture 26 Properties of liquids viscosity resistance to flow IM forces viscosity surface tension energy needed to increase surface area IM forces surface tension IM interactions are energetically favorable that is heat is required to break them the more interactions the better BUT surface molecules have fewer interactions minimize energy by minimizing surface area Sheets Page 3 Lecture 26 Sheets Page 4 Lecture 26 Kinetic energy intermolecular forces kinetic energy KE prevents molecules from interacting with each other i e KE attractive intermolecular forces IMF gas KE IMF liquid KE IMF solid KE IMF KE T energy IN heating Sheets Page 5 solid liquid gas Lecture 26 Phase changes temperature energy change Hsub Hfus Hvap Sheets Page 6 Lecture 26 Phase diagrams Go to http treefrog fullerton edu chem LS phased html phase diagram graphically summarizes conditions where equilibria exist between phases shows the relationship between the phases as functions of T P for example normal melting point P 1 atm pressure dependence of melting point normal boiling point P 1 atm pressure dependence of boiling point critical point triple point supercritical fluid coexistence curves Sheets Page 7 Lecture 26 Calorimetry See http treefrog fullerton edu chem LS coolheat html check out heating curve phase diagram experimental measure of heat flow used to determine Hrxn molar heat capacity amount of heat required to raise 1 mole of substance 1 C or 1 K an intensive variable specific heat capacity amount of heat required to raise 1 g of substance 1 C or 1 K an intensive variable for H2O C 4 184 J g C q C m T q quantity of heat measure of energy C specific heat heat capacity per gram energy mass C see BLB Table 5 2 m mass T Tfinal Tinitial m C heat capacity an extensive property that is it depends on how much stuff you have Sheets Page 8 Lecture 26 Heating curve when heat is added to a system 2 types of changes occur 1 within single phase in blue changes are q n Cp T since T kinetic energy enthalpy H molecular motion separation between molecules molecular attractions molecular order 2 between phases in red abrupt changes from one physical state to another q n Hx x melting fusion vaporization since T is constant kinetic energy is constant BUT enthalpy H molecular separation molecular attractions molecular order Sheets Page 9 Lecture 26 Example use your units very important 2 moles of ice at 25 C are heated to 125 C How much energy is needed Cp ice 37 6 J mol K 1 ice 25 C 0 C T q1 Cp water 75 3 J mol K Cp steam 33 1 J mol K 2 ice 0 C water 0 C T q2 Hfusion 6 02 kJ mol Hvapor 40 67 3 water 0 C 100 C T q3 kJ mol 4 water 100 C steam 100 C T q4 5 steam 100 C 125 C T q5 q Sheets Page 10 Lecture 26 Example A swimmer emerging from a pool is covered with a film containing 75 g of water a How much heat must be supplied to evaporate this water b Why does the swimmer feel a chill Hvapor 40 67 kJ mol water film system swimmer surroundings Sheets Page 11 Lecture 26 Coffee cup calorimeter constant pressure calorimetry heat lost by the reaction qrxn is equal in magnitude to but opposite in sign to heat gained by the solution qsoln and vice versa more also later we ll hit this again when we cover thermochemistry we can measure temperature and calculate enthalpy heat lost or gained Sheets Page 12 Lecture 26 Before next class Read HW BLB 11 3 11 5 11 6 BLB 11 4 6 31 43 45 47 50 53 56 Sup 11 5 13 Know phase changes vapor pressure boiling points concentrations dilutions Answers p 10 qtot 112 kJ p 11 qtot 169 5 kJ Sheets Page 13 Lecture 26
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