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Chapter 11 intermolecular forces- attractive forces between all molecules and atoms -these forces hold phases of matter together -strength of intermolecular.

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Presentation on theme: "Chapter 11 intermolecular forces- attractive forces between all molecules and atoms -these forces hold phases of matter together -strength of intermolecular."— Presentation transcript:

1 Chapter 11 intermolecular forces- attractive forces between all molecules and atoms -these forces hold phases of matter together -strength of intermolecular forces determines the phase of a substance at a given temperature -intermolecular forces are weaker than bonding forces b/c of distance between molecules -it takes a much higher temp to break a bond than to overcome intermolecular forces

2 Properties of Phases of Matter PhaseDensityShapeVolumeInter. Forces Solidhighdefinite strong Liquidmoderateindefinitedefinitemoderate Gaslowindefinite weak

3 Changes Between Phases

4 Which best depicts vapor emitted from a pot of boiling water? A B C BOX A

5 Types of Intermolecular Forces 1)dispersion force (London force) -caused by motion of e- -weakest of all molecular interactions -the more e-, the stronger the dispersion force -ex- helium

6 -higher molar mass = greater dispersion forces = higher boiling points -molecular shape also plays a part in the strength of dispersion forces -page 467

7 2)dipole-dipole forces -exist in all polar molecules -polar molecules have permanent dipoles that interact with the permanent dipoles of neighboring molecules *+ end of polar molecule is attracted to – end of its neighbor -this attraction is the dipole-dipole force

8 -all molecules (polar and non-polar) have dispersion forces -only polar also have dipole-dipole forces -this extra force raises melting and boiling points compared to nonpolar molecules with similar molar masses

9 Which of the following have dipole-dipole forces? 1)CO 2 -has polar bonds, but is nonpolar b/c it is linear  no dipole-dipole forces 2) CH 2 Cℓ 2 -has polar bonds and net dipole even though tetrahedral  has dipole-dipole forces 3) CH 4 -has “slightly” polar bonds, but tetrahedral  no dipole-dipole forces

10 -polarity of molecules helps determine miscibility (ability to mix) between liquids -polar is miscible with other polar molecules, nonpolar with nonpolar -“like dissolves like”

11 3)hydrogen bonding -occurs when polar molecules have hydrogen atoms bonded directly to very electronegative atoms -causes strong interaction between H and other atoms in other molecules -strongest of the first three intermolecular forces -substances with hydrogen bonding have higher melting and boiling points -water exhibits very strong H-bonding and this explains its behavior

12 -these two compounds have the same formula, but different structures which results in one having strong H-bonding and one not

13 Which one of the following compounds has a higher boiling point and why? -all have similar molar masses- similar dispersion forces -all are polar- all have dipole-dipole forces **hydrogen peroxide b/c it has H-bonding, harder to break apart

14 4)ion-dipole force -occurs when an ionic compound is mixed with a polar compound -strongest of all the intermolecular forces -common in aqueous solutions

15 -ex- salt and water

16 Summary of Intermolecular Forces

17 Results of Intermolecular Forces 1)surface tension -inward force or pull that tends to minimize the surface area of a liquid -molecules with increased intermolecular forces have increased surface tension -water has an extremely high surface tension b/c of the strong H-bonding ex- forming spherical droplets, things being able to float on water -it is difficult to break the H-bonds -will decrease by adding a surfactant (soap)

18 2)viscosity -the resistance of a liquid to flow -increases with greater intermolecular forces b/c molecules cannot flow as easily -also depends on molecular shape- higher in longer molecules b/c they can become entangled -temp plays a part- the higher the temp, the lower the viscosity

19 3)capillary action -ability of liquid to flow against gravity up a narrow tube cohesive forces- attraction between molecules of the same substance adhesive forces- attraction between molecules of different substances -if adhesive are greater than cohesive then the liquid will be drawn up -if cohesive are greater than adhesive than liquid does not rise -page 476

20 Vaporization -going from liquid to gas -need adequate energy to break free from liquid -the higher the temp, the more the liquid will vaporize -some escaped gas molecules with low energy will plunge back into molecule -this is called: Condensation -gas to liquid -opposite of vaporization

21 volatile- liquids that vaporize easily ex- nail polish remover nonvolatile- liquids that do not vaporize easily ex- motor oil Rate of vaporization will increase with: -increasing temp -increasing surface area -decreasing intermolecular forces

22 heat of vaporization (∆H vap ) -amount of heat required to vaporize one mole of a liquid -∆H vap is always positive b/c energy is absorbed heat of condensation (∆H cond ) -amount of heat required to condense one mole of a gas to a liquid -same magnitude as ∆H vap, but opposite sign b/c energy is given off

23 vapor pressure- pressure above the surface of the liquid, causes vaporization -will be lower with stronger intermolecular forces -if a container is sealed, the liquid will still vaporize and condense, just not into the atmosphere -when rate of condensation equals rate of vaporization the liquid has reached dynamic equilibrium

24 boiling point- temp at which vapor pressure equals external pressure normal boiling point- temp at which vapor pressure equals 1atm -at lower pressure, water boils at lower temp -will take longer to cook foods at locations with higher altitudes *Ex- Mt. Whitney, CA water boils at 87°C -once boiling, the liquid will not rise above boiling point until all of the water has been converted to steam

25 critical temp- the temp at which a liquid cannot exist supercritical fluid- has properties of both liquids and gases critical pressure- pressure needed to bring the liquid back at the critical temp **can be used as a solvent to extract things- CO 2 extracts caffeine from coffee beans **can be easily removed by lowering the pressure below the critical pressure and it will evaporate away

26 heat of sublimation (∆H sub ) -goes from solid to gas without passing through liquid phase ex- frozen foods deposition- gas to solid skipping liquid phase melting point- temp at which solid turns to liquid -melting is also called fusion freezing point- temp at which liquid turns to solid

27 heat of fusion (∆H fus ) -amount of heat required to melt one mole of a solid -endothermic= + heat of solidification (∆H solid ) -amount of heat required to solidify one mole of a liquid -exothermic= - -same magnitude as ∆H fus, but opposite sign b/c energy is given off -page 488

28 How much heat is required to melt 32.30g of acetone at its melting point? 32.3g C 3 H 6 O x 1 mole x 5.69kJ = 3.17kJ 1 58g 1 mole -look at heat curve page 489 *there is no temp change during conversion

29 Phase Diagrams page 491-493 -a map of the phase of a substance as a function of pressure (y-axis) and temp (x-axis) Features of a phase diagram regions- represents conditions where solid, liquid or gas is stable lines- each line or curve represents a set of temp and pressures at which the substance is at equilibrium between the two phases on either side of the line

30 triple point- unique set of conditions where all three phases exist in equilibrium critical point- where supercritical fluids exist

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