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Home , Melting, Phase (matter)

10.4 Changes Phase Changes - note structures

 fusion (): s  l : l  s  : l  g : g  l  sublimation: s  g deposition: g  s

Enthalpy – DH – DH fusion and vaporization

 DH + is endothermic  DHfus = heat of fusion = energy to convert  Heat is added, required to , energy needed to melt

 DH – is exothermic  DHvap = heat of vaporization = energy to  Heat is released, heat exits convert liquid to , energy needed to boil

 Ignore DS and DG – we do that in CHM 152  Look at Figure 10.9

Heating Curve

Why does T  The temp stays constant during melting and stay constant because all the energy is going into during fusion breaking the IMF that is holding the solid / (melting) and liquid together. vaporization?  Note and freezing point are the How is energy same temp. and condensing used between A point are also the same temp. and B, C and D?  mp = fp for = 0oC Figure 11.38  bp = cp for water = 100oC

Water 1 1 Temp chgs of state

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1 answers 10.5 Evap, VP and bp

 Xe because it is bigger, more electrons, more  Boiling – quick heating of a liquid to break IMF London force than Kr, so higher bp and turn liquid into gas. where this occurs is the bp.  CH3Cl because it is polar and CH4 is nonpolar  – no heat added, very slow,  NH3 because it has the stronger H bonding forces holding it together surface / “pop” out and float away. Only the higher kinetic energy ones pop out, so this lowers the KE of the sample left behind, thus it feels cooler. This occurs at lower temp than the bp.

10.5 Vaporizing liquid VP

 Liquid evaporates, gaseous molecules exert a  A liquid with a lower IMF will actually have a pressure () in a closed container higher VP because the molecules evaporate that can be measured as shown below easier, so more pressure  A liquid with a higher IMF will have a lower VP because it is harder for the molecules to go to the gas phase, they prefer to stay liquid, so less gas, less pressure.  So as IMF increase, VP decrease  As IMF increase, bp increase

Figure 10.11

10.6 Kinds of Kinds of Solids

 Amorphous: random arrangement (rubber)  Molecular (left): covalent molecules in an ordered arrangement (sucrose, ice); intermolecular forces hold  Ionic: ordered arrangement of (NaCl), has molecules together, low mp ionic bonds, high mp  Covalent network (right): atoms connected by covalent bonds in all directions in 3D array (quartz, ),  See Figure 10.14 high mp

2 Kinds of solids 10.11 Atomic Phase diagrams

 Metallic – has metallic bonds, mp varies,  Features of a phase diagram: conducts well, solid , , , etc  : temperature and pressure at which all three phases (s, l, and g) exist and are in equilibrium  Vaporization curve: equilibrium between liquid and gas  Melting curve: equilibrium between solid and liquid  Normal melting point: melting point at 1 atm  Normal boiling point: boiling point at 1 atm

Label Phase diagrams 27

10.11 Phase Diagram: Water Low Temp Boil Critical Temperature and Pressure

 Critical point: liquid and gas phases are indistinguishable

 Critical temperature, Tc : highest temperature at which a substance can exist as a liquid

Phase (cannot be liquified) no how much Diagram pressure is applied

 Critical pressure, Tp : minimum pressure that must be applied to bring about at the critical temperature

http://www.chm.davidson.edu/ChemistryApplets/PhaseChanges/PhaseDiagram.html

Phase Diagram: Dioxide Phase Dia-

Grams: H2O Worked Ex. 10.11, and CO2 Problems 10.17, 10.18, 19

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