States of Matter
and Intermolecular
Forces
3 Phases of Matter
 Solid
 Liquid
 Gas
How do particles move in a solid?
Solids

Have a definite shape/structure

Very little particle movement—fixed position
Liquids

Limited structure to particles

Movement is less restricted, particles can move around and collide
with each other

Conform to a container’s shape
Gases

No structure

Movement is not restricted

Particles are always in motion

Expansion occurs
Phase Changes

Physical change of a chemical compound

Change of state

Types:

Melting

Freezing

Vaporization

Condensation

Sublimation

Deposition
Evaporation/Vaporization

Liquid---gas, endothermic

Liquid molecules gain enough energy to enter the gaseous
state via breaking intermolecular forces.

Enthalpy of vaporization—

Amount of heat necessary to evaporate a liquid at constant
temperature

kJ/mole

Table 11.1 (p. 435)
Condensation

Gas-----liquid

Exothermic process
Example 1
At 25°C, how much heat is required to evaporate 175 g of methanol?
Example 2:
Which liquid in Table 11.1 (p. 435) requires the lowest amount of heat
for vaporization?
Vaporization/Condensation

Processes exist at the same time

Dynamic equilibrium is established


Rate of vaporization = rate of condensation

No net change in molecular movement
Many factors determine how long it will take for equilibrium to be
established
Vapor Pressure

Characteristic of liquid

Partial pressure of vapor when it exists with a liquid in dynamic
equilibrium under constant temperature

Dependent on liquid type and temperature at equilibrium

INCREASE vapor pressure of liquid, INCREASE temperature
Vapor Pressure Curve
Figure
11.4 p. 439
Volatile vs. Nonvolatile Liquids
1)
2)
Volatile Liquids

WEAK intermolecular forces

High vapor pressure

Ex. Gasoline, alcohols, “Whoosh Bottle”
Nonvolatile Liquids

STRONG intermolecular forces

Low vapor pressure
Whoosh Bottle Demo Video

http://www.youtube.com/watch?v=-BtFHg-lm_M
Boiling Point

Liquid characteristic

Vaporization present throughout the liquid

Point where vapor pressure = atmospheric pressure

Aids in liquid identification

Decrease atmospheric pressure with increased altitude, lowers
boiling point
Boiling Point (cont.)


Critical temperature/pressure (TC , PC)

Highest temperature with liquid and vapor present as physically different
states in equilibrium

Point where increased pressure only will result in condensation
Critical Point

Actual physical condition where critical temperature and pressure
achieved
Melting/Melting Point


Melting/freezing point

Temperature when solid “melts”

Temperature when liquid becomes solid

For water = _________
Enthalpy (heat) of fusion– Δhfusion

Amount of heat needed to convert a certain amount of a solid to a
liquid

Melting—endothermic

Freezing—exothermic (- value)
Cooling/Heating Curves
Figure
11.7 p. 444
Cooling/Heating Curves
Sublimation

Solid  Gas

Some solid compounds are volatile enough to have a vapor
pressure and convert to gas

Ex. Mothballs, dry ice

Rate of sublimation = rate of deposition

Sublimation curve

Sublimation pressure—

Pressure of a vapor existing in equilibrium with a solid
Enthalpy (heat) of sublimation
=
ΔHfusion + ΔHvapn
Homework

Chemical Bonding Study Guide

Intermolecular Forces II Worksheet—due Friday