1. Phase Changes (i.e., changes of state) -- energy changes required are related to IMFs -- melting, freezing, boiling (vaporization), condensation, sublimation, deposition (Evaporation?) heat of fusion (c f ): energy per “something” required to melt a substance -- also called... latent heat heat of vaporization (c v ): energy per “something” required to boil a substance passive process; room temp. or “fuse”or condense

2. How do magnitudes of c v and c f compare? > IMFs must be completely overcome (i.e., “broken”) KE must be increased enough to allow particles to slide, relative to each other (IMFs still in effect)

3. Heating curves are graphs of temperature v. heat added (or heat removed). -- specific heat capacity: energy req’d to change temp. of 1 _____ of a substance 1 o C (1 K) -- molar heat capacity: energy req’d to change temp. of 1 _____ of a substance 1 o C (1 K) Temp. Heat Added or Removed BP MP/FP  H = q = m c p  T  H = q = + / – m c x Within a phase: Between phases: gram mole Typical Heating Curve for a Pure Substance

4. Phase Change Constants for Water c p,ice = 2.077 J/g-K c f = 333 J/g c p,water = 4.18 J/g-K c v = 2256 J/g c p,wv = 2.042 J/g-K Find the enthalpy change when 82.4 g of ice at –13.5 o C turns to water at 72.8 o C. warm ice to 0 o C: q = m c p  T q = 82.4 (2.077) (0 – –13.5) q = 2310 J melt ice at 0 o C: q = m c f q = 82.4 (333)= 27439 J heat water from 0 o C to 72.8 o C: q = m c p  T q = 82.4 (4.18) (72.8 – 0)= 25075 J q tot =  H = 54.8 kJ

5. supercooling: temporarily cooling a liquid below its freezing point without it forming a solid -- critical temperature: the highest temperature at which a substance can be a liquid critical pressure: the pressure required to bring about liquefaction at the critical temp. heat is removed so quickly that particles have no time to assume an ordered structure as IMFs increase, crit. temp…increases The intersection of the critical temperature and the critical pressure is called the critical point.

6. Pressure cookers raise the con- fining pressure on the water, so the water boils at a higher temp. A substance’s vapor pressure is the pressure exerted by a vapor in dynamic equilibrium with its liquid or solid phase. -- as IMFs increase, VP... -- as temperature increases, VP... -- liquids that evaporate easily are said to be ______ (these have high VPs) -- boiling occurs when…VP = external pressure (usually from atmos.) -- normal boiling point (NBP): the boiling temp. of a liquid at 1 atm of pres. volatile

7. Phase Diagrams -- graphs showing the conditions under which equilibria exist between different states of matter T P SOLID LIQUID GAS 1 atm Phase Diagram for a Typical Substance critical point (CT, CP) NBPNFP/NMP triple point v.p. curve of liquid v.p. curve of solid changes in FP/MP

8. Water is NOT a typical substance. Its phase diagram differs slightly, as shown below. T P SOLID LIQUID GAS 1 atm Phase Diagram for Water supercritical fluid: how we describe a substance at or beyond its critical point s.c.f.

9. Structures of Solids amorphous solid: the particles have no orderly structure -- e.g., rubber, glass -- IMFs are highly variable, so these solids have no specific… MP

10. crystalline solid: the particles are in well-defined arrangements -- e.g., ionic and elemental metallic solids -- these melt at VERY specific temps. crystal lattice: a 3-D array of points showing the crystal’s structure The crystal lattice of sodium chloride (NaCl).

11. unit cells: the repeating units of a crystalline solid primitive (or simple) cubic body-centered cubic face-centered cubic 1 atom unit cell 2 atoms unit cell 4 atoms unit cell “continuous atomage”