Outline for Today Friday, Nov. 30 Chapter 11: Intermolecular Forces - - PowerPoint PPT Presentation

Outline for Today

Friday, Nov. 30

• Chapter 11: Intermolecular Forces and Liquids
• Phase Changes
• Vapor Pressure
• Phase Diagrams
• Chapter 13: Properties of Solutions

1

Phase Changes

Heating Curves and Phase Changes

Example Problem: Enthalpy

• f Phase Changes
• How much heat is required to convert 100. g of ice that is

at -10 oC to steam at 120 oC? Cp ice 4.19 J/(g K) Cp liquid water 4.18 J/(g K) Cp steam 2.00 J/(g K) ∆Hfus 333.55 J/g ∆Hvap 2257 J/g

Heat for Phase Changes Heat for Changing Temperature

Vapor Pressure

• Vapor Pressure: the partial pressure of the vapor when it

is in dynamic equilibrium with the liquid

• Dynamic Equilibrium: Two opposing processes occur

simultaneously at equal rates gas ➞ liquid liquid ➞ gas

At equilibrium, both processes are happening at the same time!

Dynamic Equilibrium and Vapor Pressure

Volatility

• Volatility: How easily a

liquid evaporates.

• A molecule is more volatile

and has a higher vapor pressure if it has weaker intermolecular forces.

LIQUID Gas

phase transition

Volatility Examples

• Why does hot water evaporate more quickly than cold

water?

• Why does liquid nitrogen evaporate more quickly than

water?

How do Vapor Pressure and Boiling Point Relate?

Read the chart to rank the molecules by increasing vapor pressure at a given temperature. Rank the molecules by IMF Rank the molecules by Boiling Point. No Chart? The lower the boiling point, the higher the vapor pressure!

How do Vapor Pressure and Boiling Point Relate? Clausius-Clapeyron Equation

ln(P) = −∆Hvap R · 1 T + C

Phase Diagrams

Phase Diagrams: How To Read Them

Given two independent variables: P and T… what is the dependent variable, the phase or state of matter?

Phase Diagram for CO2

Phase Diagram for H2O