13 152-2-25-2011

# 11• Given: for water

– 625 mm Hg bp 94.5oC ∆H vap = 40.7 kJ/mol ? Bp?

At 1.75 atm

– What do you know? 2P’s and 1T and ∆H vap

– Be sure P units are consistent and T in K, ∆H vap in

J (not kJ) – to match with R unitsJ (not kJ) – to match with R units

– ln(P2/P1) = ∆H vap /R (T1-1-T2

-1)

London (dispersion) Forces

Induced (temporary) dipoles

Uneven charge distribution in one induces a charge distribution

in the other

Caused by movement of electrons in electron clouds

electron clouds like “nerf” balls

All atoms have these forces – explains the condensation of inert

gases

Polarizability – ease of distorting electron clouds – larger atoms, Polarizability – ease of distorting electron clouds – larger atoms,

outer electrons held less tightly

Increasing London forces means higher boiling points

larger atoms He vs Xe

Larger molecules CH4 vs C3H8

Longer molecules C(CH3)4 vs C5H12

Higher boiling points – remain liquid at higher temps

Cis and trans bonds in fats – cis lower mp -- trans higher IMF

Permanent dipoles – polar molecules

Special case of dipoles

H-bond

CHM 152

2-23-2011

Cis and trans bonds in fats – cis lower mp -- trans higher IMF

Find sp2 C’s

Compare 4 C alkane, alcohol, thiol

• OWL IMF

• 9.3 a-e

• Book: ch 9: 25-38

• Break/test• Break/test

• On-line video and questions WATER

– See assignment!!

• Read rest of chapter 9 for Monday