Chapter 12 (Liquids, Solids, & Intermolecular Forces) Intermolecular Forces: • Forces that hold solids and liquid together • Give rise to observable phenomena in liquids o Surface Tension: Net inward force caused by attraction of liquid particles o Viscosity: a measure of a fluid's resistance to flow o > Intermolecular forces : > Surface tension & > Viscosity. • If similar intermolecular forces between two liquids, they are likely to be Miscible in each other. (Like Dissoloves Like) Three types of intermolecular forces: 1) Dispersion Forces • Weakest Intermolecular force • All particles exhibit this force to some degree • Brought on by the formation of temporary dipoles between particles 2) Dipole-Dipole Interactions • Intermediate strength force • Brought about via the lining up of permanent dipoles within a molecule3) Hydrogen Bonding • Strongest (by far) Intermolecular Force • Occurs between Oxygen, Nitrogen, & Fluorine atoms and the hydrogens connected to them. Types of crystalline solids:Types of Atomic solids: Liquids: Evaporation & Condensation: • In a given liquid sample, the particles will all have different kinetic energies. There will always be a fraction of these particles which have sufficient energy to achieve Escape Velocity. • Rate of evaporation depends upon three factors: o Surface Area o Temperature o Intermolecular force strength of the liquid particlesDefinitions: ! Volatility: The relative rate at which a liquid evaporates. ! Vapor Pressure: The pressure exerted by the molecules of a given vapor (closed system). ! < Vapor Pressure means < Volatility, > Boiling Point, & > Intermolecular forces. ! > Vapor Pressure means > Volatility, < Boiling Point, & low Intermolecular forces. • Boiling Point: the boiling point of a liquid is the temperature at which its vapor pressure is the same as atmospheric pressure. The energy of evaporation & condensation: q = m·∆∆∆∆Hvap ! Evaporation is endothermic & Condensation is exothermic ! The process can be quantified as the “Heat of Vaporization” (∆Hvap) o Defined as the amount of energy required to vaporize a given amount (ie: g or mol) of liquid at its boiling point. The energy melting & freezing: q = m·∆∆∆∆Hfus ! melting is endothermic & freezing is exothermic ! The process can be quantified as the “Heat of Fusion” (∆Hfus) o Defined as the amount of energy required to melt a given amount (ie: g or mol) of solid at its melting point. The energy of changes in temperature within a state: ! Given as Heat Capacity (c) q = m·c·∆∆∆∆TMelting Point Boiling Point ∆∆∆∆Hfus (J/g) ∆∆∆∆HVap (J/g) Heat Capacity (c) (J/g·oC) Solid (ice) Liquid (water) Gas (steam) Water 0oC 100oC 334 J/g 2261 J/g 2.09 J/g·oC 4.18 J/g·oC 1.84 J/g·oC q = m · c · ∆∆∆∆T Used in describing a temperature increase within a specific phase (ie: solid, liquid, gas). q = m · ∆∆∆∆Hfus Used in describing a phase change between a solid and a liquid. q = m · ∆∆∆∆Hvap Used in describing a phase change between a liquid and a gas. ∆Hfus, ∆Hvap, and Heat Capacity (c) can be combined to describe the journey of a solid below its freezing point to a gas above the substance’s boiling