Chapter 12: Liquids & Solids

Question 1

Surface tension

Answer 1

Elastic force in the surface of a liquid

The amount of energy required to strech or increase the surface of a liquid by a unit area

Strong intermolecular forces = high surface tension

Question 2

Capillary action

Answer 2

More pronounced in a cylinder with small diameter

Miniscus forms either a concave (U-shaped) or convex (dome-shaped) curve at the liquid’s surface due to cohesion and adhesion

Question 3

Cohesion

Answer 3

Attractions between like molecules

Question 4

Adhesion

Answer 4

(Think tape: sticks to other material)

Attractions between unlike molecules

Question 5

Viscosity

Answer 5

A measure of a fluid’s resistance to flow

As T increases, viscosity decreases

Question 6

Vapor pressure

Answer 6

Depends upon magnitude of intermolecular forces

High vapor pressure = volatile substances

Question 7

Evaporation or vaporization

Answer 7

Change of phase: from liquid to gas

*Initially more rapid than condensation

Question 8

Condensation

Answer 8

Change of phase: gas to liquid

Can occur when gas strikes liquid surface and becomes trapped by intermolecular forces

*Initially slower than evaporation

Question 9

Dynamic equilibrium

Answer 9

When a forward process and reverse process occur at the same rate

Both processes going on (dynamic)

Number of gas molecules in the gas phase at any point in time doesn’t change (equilibrium)

Question 10

Equilibrium vapor pressure

Answer 10

The pressure exerted by the molecules that have escaped to the gas phase, once the pressure has stopped increasing

Question 11

Boiling point

Answer 11

The temperature at which its vapor pressure equals the external pressure

Question 12

Melting point

Answer 12

The temperature at which the energies of individual particles enable them to break free of their fixed positions in the solid – allowing them to flow past one another

Stronger intermolecular forces = higher melting point

Question 13

Crystalline solid

Answer 13

Rigid and long-range internal order/structure of molecules/particles

Question 14

Lattice structure

Answer 14

Arrangement of particles in a crystalline solid

Depends on the nature and size of the particles involved

Question 15

Unit cell

Answer 15

The basic repeating structural unit of a crystalline solid

Question 16

Lattice point

Answer 16

Each particle within a unit cell

Question 17

Simple/primitive cubic cell

Answer 17

8 lattice points (particles)

1/8 (8 particles) = 1 whole particle in simple cubic cell

Coordination number: 6

Question 18

Coordination number

Answer 18

The number of atoms/particles surrounding an atom/particle in a crystal lattice

Larger coordination # = more tightly packed cell

Question 19

Body-centered cubic cell

Answer 19

9 lattice points (8 corners, 1 center)

1/8 (8 corner lattice points) + 1 = 2 whole particles in cell

Coordination number:
8

Question 20

Face-centered cubic cell

Answer 20

8 corners + 6 sides = 14 particles/lattice points

1/8 (8 corners) + 1/2 (6 sides) = 4 whole particles in cell

Coordination number: 12

Question 21

Molar heat of vaporization ΔH_vap

Answer 21

Amount of heat required to vaporize a mole of substance at its boiling point

kJ/mol

Question 22

Critical temperature T_C

Answer 22

Particular temperature at which a substance in its gas phase cannot be liquefied, no matter how great the applied pressure

Question 23

Critical pressure C_P

Answer 23

The minimum pressure that must be applied to liquefy a substance at its critical temperature

Question 24

Supercritical fluid

Answer 24

A fluid at a temperature and pressure that exceed critical temperature and pressure

Temperatures above critical temperature = no longer a distinction between gas and liquid phases, there’s simply a fluid (plasma)

Used as solvents in many industrial applications

Question 25

Fusion

Answer 25

Melting – phase change of solid to liquid

Question 26

Freezing point

Answer 26

AKA melting point

Temperature at which solid and liquid phases coexist at equilibrium

Question 27

Normal melting/freezing point

Answer 27

The temperature of melting/freezing at 1 atm

Question 28

Molar heat of fusion ΔH_fus

Answer 28

Energy (kJ/mol) required to melt 1 mole of a solid

*MUCH smaller than ΔH_vap because solids & liquids are more alike than liquids & gases

Question 29

Supercooling

Answer 29

Liquid is temporarily cooled to below its freezing point

Occurs when heat is removed from a liquid so rapidly that the molecules literally have no time to assume the ordered structure of a solid

Unstable - stirring or adding small “seed” crystal solidifies sample quickly

Question 30

Sublimation

Answer 30

Phase change from solid to gas

Thus, solids can have vapor pressure

Question 31

Deposition

Answer 31

Phase change – vapor phase to solid phase

Question 32

Molar enthalpy of sublimation ΔH_sub

Answer 32

Amount of energy (kJ/mol) required to sublime 1 mole of a solid

ΔH_sub = ΔH_vap + ΔH_fus

Question 33

Phase diagram

Answer 33

Summarizes conditions (T & P) at which a substance exists in its various phases

Separated by phase boundary lines

Question 34

Triple point

Answer 34

The point on a phase diagram at which all three phase boundary lines meet

The only combination of T & P at which all three phases of a substance can be in equilibrium with each other

Question 35

Critical point

Answer 35

Point at which the liquid-vapor phase boundary line abruptly ends

This corresponids with the critical temperature and pressure (C_T and C_P)