1. liquids solids and phase changes le3 reviewer

8/18/2019 1. Liquids Solids and Phase Changes LE3 Reviewer

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Chem 16 3rd

Long Exam Reviewer May 2015

UP Psych Soc Literary Archives Committee Liquids, Solids andPhase Changes

LIQUIDS, SOLIDS AND PHASE CHANGES

PHYSICAL STATES

Intramolecular forces are bonding forcesthat exist within each molecule andinfluence the substance’s chemical

properties Intermolecular forces are nonbonding

forces that exist between the moleculesand influence the physical properties ofthe substance

Kinetic Molecular View

PHASE CHANGES

Evaporation is also known asvaporization and melting is also calledfusion

Condensing and freezing are exothermicchanges while melting and vaporizing areendotherming changes

For pure substances, each phase changehas a specific, standard enthalpy changeper mole. For vaporization, it’s called theheat of vaporization (∆H °vap) and forfusion, it is the heat of fusion (∆H °fus)

The reverse processes, condesing andfreezing, have enthalpy changes of thesame magnitude but opposite sign

The heat of sublimation(∆H °subl) is the enthalpychange when 1 mol ofsubstance sublimes

The Clausius-Clapeyronequation gives us a way of finding ∆H vap.It is given by:

Where P is vapor pressure, R is the

universal gas constant (8.314

J/mol·K) and T is temperature

PHASE DIAGRAMS

Combines the

liquid-gas, solid-

liquid and solid-

gas curves to

describe phase

changes of a

substance at

various conditions

of temperature

and pressure

Each region

corresponds to one phase of the

substance. A particular phase is stabe for

any combination of pressure and

temperature within its region.

The lines show the pressure and

temperature at which the two phases oneither side exist in equilibvrium

At the critical point, the liquid and vapor

densities have reached critical

temperature (T c ) and critical pressure (P c ).

At this point, the two densities are equal

and the phase boundary disappears


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The triple point represents the pressure

and temperature at which the three

phases are in equilibrium

INTERMOLECULAR FORCES (IMF)

When an ion and a nearby polar molecule(dipole) attract each other, an ion-dipoleforce results

When polar molecules lie near oneanother, their partial charges give rise todipole-dipole forces: the positive pole ofone molecule attracts the negative pole ofanothero Higher boiling point for compounds

consisting of polar molecules ascompared to compounds of nonpolarmolecules with the same molar mass

The hydrogen bond (H bond) is a type ofdipole-dipole force that arises from an Hatom bonded to a small, highlyelectronegative atom with lone e- pairs(usually N, O & F)

A nearby electric field can induce adistortion in an e- cloud, pulling e- densitytoward a (+) charge or away from a (-) oneo For a nonpolar molecule, this

distortion creates a temporary,induced dipole moment; for a polarmolecule, it enhances the dipole

moment already presento Polarizability is the ease with which

the e- cloud of a particle can bedistorted

Ion-induced dipole and dipole-induceddipole are the 2 types of charge-induceddipole forces

Dispersion (London) forces areresponsible for the condensed states ofnonpolar substances. They are caused bymomentary oscillations of e- charge inatoms and are present in all particleso Dispersion forces (DF) are

instantaneous dipole-induced dipoleforces. They contribute to the overallenergy of attraction of all substances

o For polar molecules, relative strengthof DF depends the polarizability of theparticles. For nonpolar, it depends onmolecular shape

PROPERTIES OF LIQUIDS

Surface tension is the energy required toincrease the surface area by a unitamount. In general, the stronger theforces between the particles in a liquid,the greater the surface tension

Capillarity is the rising of a liquid througha narrow space against the pull of gravity.It results from a competition between theIMF within a liquid (cohesive forces) andthose between the liquid and the tube

walls (adhesive forces)o Right – adhesive > cohesive

Left – cohesive > adhesive

A liquid’s resistance to flow is calledviscosity. Liquid viscosities are highercompared to gases because IMF operateover shorter distances. Viscositydecreases with heating

The boiling point of a substance is thetemperature at which the vapor pressure,the pressure exerted by a vapor atequilibrium, equals the external pressureand the liquid turns into vapor

SOLIDSTypes

Based on the orderliness of shapes andparticles o Crystalline solids have a well-defined

shape due to the orderly arrangement

of their particleso Amorphous solids have poorly

defined shapes because their particleslack order

Structure

The points (centers of identical particles)form a regular pattern throughout thecrystal called the crystal lattice. The


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lattice consistsof all points withidenticalsurroundings

The unit cell isthe smallest

repeating unit ofa crystal

The coordination number of a particle isthe number if nearest neighbourssurrounding it

There are 7 crystal systems but we willfocus on the cubic system, which givesrise to the cubic lattice o In a simple cubic unit

cell, the centers of 8particles define thecorners of a cube. The

coordination number ofeach particle is 6. Asimple cubic unit cellcontains 8(1/8) = 1 particle

o In the body-centeredcubic unit cell, there isan additional particle inthe center of the cube.Coordination number = 8.

A BCC unit cell contains8(1/8) + 1 = 2 particles

o A face-centered cubic

unit cell has simple cubicstructure but with anadditional particle in eachface. It has 8 corners and6 faces. Coordinationnumber = 12. A FCC unitcell contains 8(1/8) +6(1/2) = 4 particles

Bonding

The electron-sea model proposes that allthe metal atoms in a sample pool their

valence e- to form an e- “sea” that isdelocalized throughout the piece. Thevalence e- are shared among all theatoms in a sample

According to the band theory, the highestenergy e- occupy either a partially filled ora filled band that overlaps an empty band

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