1112 Equilibrium Phases Med

7/28/2019 1112 Equilibrium Phases Med

http://slidepdf.com/reader/full/1112-equilibrium-phases-med 1/18

Liquid-Vapor Equilibrium

(Intermolecular Forces and Liquids and Solids)

Green/Damji: 17.1Chang: Chapter 11

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.



E v a p o r a t i o

n

Greatest

Order

Least

Order

11.8

C o n d e n s a t i o n

Focus onEvaporation and

Condensation

Write an equation for the

equilibrium between liquid

water and its vapor:

Is evaporation an

endothermic or exothermic

process?



Before

Evaporation

At

Equilibrium

11.8



The equi l ibr ium vapor pressu re is the vapor pressure

measured when a dynamic equilibrium exists between

condensation and evaporation

H2O (l ) H2O (g )

Rate of

condensation

Rate of

evaporation=

Dynamic Equilibrium

11.8



Factors affecting the vapor pressure

• SURFACE AREA

increasing surface area only meansequilibrium is reached faster

• TEMPERATURE



11.8

T2 > T1

What is the name of this

diagram? Why is it

important?


http://slidepdf.com/reader/full/1112-equilibrium-phases-med 7/1811.8

Vapor Pressure Versus Temperature

Patterns? Why?



Enthalpy o f vaporizat ion (DH vap) is the energy required to

vaporize 1 mole of a liquid at its boiling point.

Enthalpy of vapor izat ion : physic al proc ess (phase change) as

______________________: chem ical reac t ion

11.8



The relat ionship between vapo r pressu re and temperature

can be exp ressed mathematical ly – NOT req’d by IB

ln P = -DH vap

RT + C

Clausius-Clapeyron Equation P = (equilibrium) vapor pressure

T = temperature (K)

R = gas constant (8.314 J/K•mol)

11.8

Vapor Pressure Versus Temperature

C = integration constant



Heating Curve

Why are there plateaus on this graph?



The boi l ing po int is the temperature at which the

(equilibrium) vapor pressure of a liquid is equal to the

external pressure.

The normal boi l ing po int is the temperature at which a liquid

boils when the external pressure is 1 atm.

11.8



What are the three primary intermolecular forces?

List in order of increasing strength.



The boi l ing po int and enthalpy of vapor izat ion are

influenced by intermolecular forces…

Compound Enthalpy of

vaporization

in kJ mol-1

Boiling Point

in K

Intermolecular

Forces

methane

CH4

9.0 109

methoxy

methane

CH3OCH3

27.2 248

ethanolCH

3CH

2OH

38.6 352



State the relationship between intermolecular

forces and enthalpy of vaporization.

State the relationship between intermolecular

forces and boiling point.





A phase diagram summarizes the conditions at which a

substance exists as a solid, liquid, or gas.

Phase Diagram of Water

11.9



Effect of Increase in Pressure on the Melting Point

of Ice and the Boiling Point of Water



Textwork 17.1

Read 17.1 on pp 192-193

Address each of the learning objectives on p.

192 by taking notes that directly relate to the

objectives.

Due on __________________

Documents

1112 Equilibrium Phases Med