January 27th 2017 Chapter 12 Chapter 11 12 HW due Friday Feb 3rd Exam 1 Wednesday Feb 8th iClicker Course site D2L Phase Diagrams Effect of Pressure and Temperature on Physical State Phase diagram for CO2 At the critical point the densities of the liquid and gas phases become equal At the triple point all three phases are in equilibrium Phase diagram for H2O The solid liquid line slants to the left for H2O because the solid is less dense than the liquid Water expands on freezing Which of the following statements is correct A As temperature increases vapor pressure decreases B The triple point is the point at which there is no phase boundary C Vapor pressure increases with weaker intermolecular forces D The Clausius Clapeyron equation can be used to calculate the enthalpy of formation E Phase changes are always irreversible 12 3 Types of Intermolecular Forces Physical behavior of the phases and their changes due primarily to intermolecular forces which arise from the attraction between molecules with charges partial charges and or induced charges Intermolecular forces are relatively weak How Close Can Molecules Approach Each Other van der Waals radius closest distance between two adjacent nuclei of identical nonbonded atoms Periodic trends in covalent and van der Waals radii in pm Table 12 2 Comparison of Bonding and Nonbonding Intermolecular Forces Table 12 2 Comparison of Bonding and Nonbonding Intermolecular Forces Table 12 2 Comparison of Bonding and Nonbonding Intermolecular Forces Figure 4 2 Table 12 2 Comparison of Bonding and Nonbonding Intermolecular Forces solid The positive pole of one polar molecule attracts the negative pole of another liquid Temperature K Table 12 2 Comparison of Bonding and Nonbonding Intermolecular Forces Molecule with H atom bonded to small highly EN atom with lone pairs O N F attracted to lone pair on N O or F of another molecule H hydrogen bond acceptor O O F hydrogen bond donor hydrogen bond acceptor hydrogen bond acceptor H F N hydrogen bond donor H N hydrogen bond donor Table 12 2 Comparison of Bonding and Nonbonding Intermolecular Forces A When atoms are far apart they do not influence one other B When atoms are close together the instantaneous dipole in one atom induces a dipole in the other C The process occurs throughout the sample Table 12 2 Comparison of Bonding and Nonbonding Intermolecular Forces Dispersion London forces arise when an instantaneous dipole in one particle induces a dipole in another resulting in an attraction between them Dispersion forces are stronger for more polarizable particles In general larger particles experience stronger dispersion forces than smaller ones Dispersion forces are stronger for more polarizable particles In general larger particles experience stronger dispersion forces than smaller ones Molecular shape effects dispersion forces There are more points at which dispersion forces act There are fewer points at which dispersion forces act Which of the following substances exhibits H bonding a C2H6 b CH3OH c NH3 d Both a and b e Both b and c Molecule with H atom bonded to small highly EN atom with lone pairs O N F attracted to lone pair on N O or F of another molecule 12 4 Properties of the Liquid State Surface Tension units J m2 energy required to increase the surface area The stronger forces between the particles the higher the surface tension 12 4 Properties of the Liquid State Capillarity rising of liquid along container walls against pull of gravity Competition between intermolecular forces within the liquid and adhesive forces between liquid and walls 12 4 Properties of the Liquid State Viscosity resistance of a fluid to flow Intermolecular attractions that impede the movement of molecules past each other Viscosity decreases with increasing temperature