Liquid-Vapor Equilibrium (Intermolecular Forces and Liquids and Solids)

Green/Damji: 17.1Chang: Chapter 11

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Eva

pora

tion

GreatestOrder

LeastOrder

11.8C

onde

nsat

ion

Focus on Evaporation and

Condensation

Write an equation for the equilibrium between liquid

water and its vapor:

Is evaporation an endothermic or exothermic

process?

BeforeEvaporation

At Equilibrium

11.8

The equilibrium vapor pressure is the vapor pressure measured when a dynamic equilibrium exists between condensation and evaporation

H2O (l) H2O (g)

Rate ofcondensation

Rate ofevaporation=

Dynamic Equilibrium

11.8

Factors affecting the vapor pressure

• SURFACE AREA increasing surface area only means equilibrium is reached faster

• TEMPERATURE

11.8

T2 > T1

What is the name of this diagram? Why is it

important?

11.8

Vapor Pressure Versus Temperature

Patterns? Why?

Enthalpy of vaporization (DHvap) is the energy required to vaporize 1 mole of a liquid at its boiling point.

Enthalpy of vaporization : physical process (phase change) as

______________________: chemical reaction

11.8

The relationship between vapor pressure and temperature can be expressed mathematically – NOT req’d by IB

ln P = -DHvap

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

11.8

Heating Curve

Why are there plateaus on this graph?

The boiling point is the temperature at which the (equilibrium) vapor pressure of a liquid is equal to the external pressure.

The normal boiling point 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 boiling point and enthalpy of vaporization are influenced by intermolecular forces…

Compound Enthalpy of vaporizationin kJ mol-1

Boiling Pointin K

Intermolecular Forces

methaneCH

4

9.0 109

methoxymethaneCH

3OCH

3

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

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 __________________