13 152-2-25-2011
DESCRIPTION
intro IMFTRANSCRIPT
# 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