Ch. 13: Liquids & Solids

Ch. 13: Liquids & Solids

Meniscus: the curved surface of a liquid in a container (A could be water and B could be mercury) – see below

Adhesion vs. Cohesion

Adhesion – the attraction of a substance for other substances (the walls of its container, possibly)

Cohesion – the attraction of a substance for itself

Properties of liquids• Capillary action.Capillary action.

MercuryCohesive is largerthan adhesive.

WaterAdhesive is largerthan cohesive.

Capillary tube

meniscus

• ViscosityViscosity• Resistance to flow.

• This increases with increased intermolecular attractions.

• Also, liquids composed of long, flexible molecules can entwine, resulting in increased viscosity - motor oil.

Properties of liquids

CH3CH2CH2

OH

CH3CH CH2

OHOH

CH2CH CH2

OHOHOH

Increasing viscosity

Properties of liquids

• Surface TensionSurface Tension• Force in the surface of a liquid that makes the area

of the surface as small as possible.

Molecules at thesurface interactonly with neighborsinside the liquid.

Molecules at thesurface interactonly with neighborsinside the liquid.

Properties of liquids• VaporizationVaporization• The formation of a gas from a liquid.

• At any temperature, at least a few of the molecules in the liquid are moving fast enough to escape.

initially equilibrium

after sometime

molecules leave andRe-enter liquid at

the same rate

molecules leave andRe-enter liquid at

the same rate

Equilibrium• A state where the forward and reverse

conditions occur at the same rate.

DynamicEquilibrium

I’m in staticequilibrium.

Vapor Pressure and boiling point

• Equilibrium vapor pressureEquilibrium vapor pressure• The pressure of a vapor in equilibrium with

a liquid.• It depends on:It depends on:• the intermolecular forces in the liquid.• temperature.• It is independent of:It is independent of:• the volume of the liquid or vapor• the surface area of the liquid

Boiling Points

• Boiling pointBoiling point - temperature where the vapor pressure equals atmospheric pressure.

Boiling point of water at various elevations

City Elevation BP (oC) San Francisco Sea level 100.0 Salt Lake City 4,390 95.6 Denver 5,280 95.0 La Paz, Bolivia 12,795 91.4 Mount Everest 20,028 76.5

Boiling point of water at various elevations

City Elevation BP (oC) San Francisco Sea level 100.0 Salt Lake City 4,390 95.6 Denver 5,280 95.0 La Paz, Bolivia 12,795 91.4 Mount Everest 20,028 76.5

This is the reason that cake mixes includehigh altitude baking instructions.

Heating Curve

Phase Diagramssupercriticalfluid regionsupercriticalfluid region

TcTc

solidsolidliquidliquid

gasgas

PcPc

temperaturetemperature

pre

ssu

rep

ress

ure Critical

pointCriticalpoint

Phase Diagram of H2O

Phase Diagram of CO2

Boltzmann Curve

• As the temperature is increased, a higher fraction of molecules will have a kinetic energy that is greater than the energy needed for a phase change.

T1 < T2 < T3

T1 < T2 < T3

Kinetic energy

Fract

ion o

f m

ole

cule

sH

avin

g k

ineti

c energ

y

T3

T2

T1Ea

Allotropes of Carbons

• Allotrope: different forms of the same element

• Repeating units of covalently bonded carbon atoms.

GraphiteGraphite

Networks of Carbon

Diamond Buckminster Fullerene

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Carbon Nanotube