Notes from Progress Check 2 o 5000 cesium atoms can form 5000 molecular orbitals 2500 orbitals of these will be populated by pairs of electrons Explains conduction band 0 C all electrons are below this point but as things warm up they move above Fermi level to move electrons and positive holes section 13 3 o Electrostatic and obey coulombs law increase with smaller size getting charges closer together increasing the charge o Radius of ions example 13 3 o Thermochemical question Hess s law 1 Atomization of sodium solid to a gas Na s Na g H 107 3 kJ mol 2 Ionization energy of Na Na g Na g e H 495 9 3 Formation of solid Na2O 2 Na g O2 g Na2O s Hf 418 4 Formation of O g from O2 g O2 g O g Hf 249 1 5 First e attachment enthalpy of O O g e O g H 141 0 6 Lattice energy 2Na g O2 g Na2O Hlat 2481 Want to know O e O2 H Flip 5 H 141 0 Flip 4 H 249 1 Keep 3 H 418 Flip 6 H 2481 Flip and double 1 H 2 107 3 Flip and double 2 H 2 495 9 End up with O g e O2 g H Formation reaction endo or exo reaction that produces 1 mol of the product Making ice cream Have to use a lot of salt lowered freezing point of water below its normal freezing point supercooled water salt solution o Same reason we throw salt on roads ice melts because it has a lower melting point hopefully it evaporates quickly before it refreezes Colligative properties Clicker Physical characteristics of a solution that depend on A the types of particles in the solution B the concentration of particles in the solution C the types and concentrations of particles in solution Colligative properties physical characteristic of a solution that depend on concentration of particles in solution and not on their identity o Slight variability based on what the particles are o If replacing to solute solvent that is much stronger or weaker little bit of a variability but is very small usually 0 5 o Can be held as pretty much true Colligative properties include o Vapor pressure lowering o Boiling point elevation o Freezing point depression o Osmotic pressure Vapor pressure lowering o Consider a solution where 85 of the molecules are solvent other 15 are solute o Vapor pressure occurs of dynamic equilibrium between solvent particles in liquid phase and solvent particles in the gas phase o Solute only exists in liquid phase o Changed the number of particles that can get into the gas phase actually at surface of liquid that could get into gas phase but they have to have the energy to get there o Decreased rate of liquid going into gas phase which lowers vapor pressure o Clicker what is the vapor pressure of a solution that is 30 3 w w ethylene glycol MW 62 07 g mol in water at 90 C The vapor pressure of pure water is 525 8 torr at 90 C Psolvent Xsolvent P solvent Assume 100 g solution 30 3 g ethylene glycol 69 7 g water X mol A total mol solution so you have to convert masses to moles 0 488 mol ethylene glycol 3 87 mol water total 4 36 mol X H2O 3 87 mol 4 36 mol 0 888 P H2O 0 888 525 8 torr 466 7 torr o Assumptions based on what is given Molar L of solution by weight w w 100 g Molal kg of solvent weight by volume 100 mL Need density to convert L of solution to mass of solution Clicker Eugenol a compound found in nutmeg and cloves has the formula C10H12O2 What is the boiling point of a solution containing 0 144 g of eugenol dissolved in 10 0 g of benzene The K bp for benzene is 2 53 C m and the normal boiling point is 80 10 C o o o Tbp Kbp x m 0 00088 mol 0 01 kg 0 088 m x 2 53 0 22 C 80 10 C 0 22 C 80 32 C Clicker Today s lowest temp in Athens was 12 F 11 C What is the minimum concentration for the radiator fluid in your car so that the solution doesn t freeze Radiator fluid is ethylene glycol MW 62 07 g mol dissolved in water The Kfp for water is 1 86 C m o o Tf 11 C Tf 11 C m 11 C 1 86 C m 5 91 m mol L Osmotic Pressure water flows from region of low solute concentration high water concentration to region of high solute concentration low water concentration push down tube to keep water from flowing into the bag water flows from low osmotic pressure to high osmotic pressure amount of pressure that needs to be applied to stop that flow can be enough to make flow go the opposite direction