Intermolecular Forces and Liquids

1. Intermolecular Forces and Liquids Chapter 12

2. Kinetic Molecular Theory Gas molecules are • _______________________________, • _______________________________, and • _______________________________. • Liquids and solids are quite different!

3. A ________________ is a homogeneous part of the system in contact with other parts of the system but separated from them by a well-defined boundary. 2 Phases Solid phase - ice Liquid phase - water Characteristic Properties of Gases, Liquids, and Solids

4. Generally, _____molecular forces are much weaker than _____molecular forces. _______________________ Forces __________________ forces hold atoms together in a molecule. _____________forces are attractive forces between molecules. • Intermolecular vs Intramolecular • 41 kJ to vaporize 1 mole of water (inter) • 930 kJ to break all O-H bonds in 1 mole of water (intra) “Measure” of intermolecular force boiling point melting point DHvap DHfus DHsub

5. Orientation of Polar Molecules in a Solid Intermolecular Forces _________________ Forces ______________ forces between polar molecules

6. Ion-Dipole Interaction Intermolecular Forces ________________ Forces _________ forces between an ion and a polar molecule

7. Intermolecular Forces ___________________ Forces ____________________ forces that arise as a result of temporary dipoles induced in atoms or molecules ion-induced dipole interaction dipole-induced dipole interaction

8. Intermolecular Forces Dispersion Forces Continued ____________________________ is the ease with which the electron distribution in the atom or molecule can be distorted. • Polarizability _____________ with: • greater number of electrons • more diffuse electron cloud Melting Points of Similar Nonpolar Compounds Dispersion forces usually ______________ with molar mass.

9. O O S What type(s) of intermolecular forces exist between each of the following molecules? HBr CH4 SO2

10. or … … H H B A A A Intermolecular Forces _________________ Bond The _________________ is a special __________________ interaction between they hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom. A & B are ____, ____, or ____

11. Decreasing molar mass Decreasing boiling point Why is the hydrogen bond considered a “special” dipole-dipole interaction? p.375

12. Properties of Liquids ______________________ is the amount of energy required to stretch or increase the surface of a liquid by a unit area. Strong intermolecular forces High surface tension p.376

13. Adhesion Cohesion Properties of Liquids __________________________________ is the intermolecular attraction between like molecules _________________ is an attraction between unlike molecules p.377

14. Properties of Liquids ________________ is a measure of a fluid’s resistance to flow. Viscosity of Some Common Liquids at 20ºC ____________ intermolecular forces _________ viscosity p.378

15. Maximum Density ____0C Water is Unique! Density of Water Ice is __________ than water

16. Least Order Greatest Order T2 > T1 Condensation Evaporation Deposition Sublimation Freezing Melting

17. H2O (l) H2O (g) Dynamic Equilibrium Rate of evaporation Rate of condensation = The ______________________ vapor pressure is the vapor pressure measured when a dynamic equilibrium exists between condensation and evaporation p.389

18. At Equilibrium Before Evaporation

19. ln P = - DHvap + C RT ____________________________________ (DHvap) is the energy required to vaporize 1 mole of a liquid. Clausius-Clapeyron Equation P = (equilibrium) vapor pressure T = temperature (K) R = gas constant (8.314 J/K•mol)

20. The ___________________ is the temperature at which the (equilibrium) vapor pressure of a liquid is equal to the external pressure (on the surface of the liquid). The ________________________ is the temperature at which a liquid boils when the external pressure is 1 atm. Molar Heats of Vaporization for Selected Liquids remember

21. The ____________________________________ (Tc) is the temperature above which the gas cannot be made to liquefy, no matter how great the applied pressure. Critical Temperatures and Critical Pressures of Selected Substances The ______________ (Pc) is the minimum pressure that must be applied to bring about liquefaction at the critical temperature.

22. H2O (s) H2O (l) The ___________ point of a solid or the _____________ point of a liquid is the temp-erature at which the solid and liquid phases coexist in equilibrium Freezing Melting p.395

23. ______________________ (DHfus) is the energy required to melt 1 mole of a solid substance. Molar Heats of Fusion for Selected Substances remember

25. H2O (s) H2O (g) _________________________ (DHsub) is the energy required to sublime 1 mole of a solid. Deposition Sublimation DHsub = DHfus + DHvap ( Hess’s Law)

26. A __________________ summarizes the conditions at which a substance exists as a solid, liquid, or gas. Phase Diagram of Water Triple Point

27. The _______________________ is the only temperature and pressure where all three phases can exist in equilibrium. p.395

28. Triple Point