Physical Chem Lecture Jan 9
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Jan 9 2012
Physical Chemistry Lecture Chapter 12
Attractive forces: interactions between atoms, due to charges on atoms, or due to the
electrons that they share.
Within molecules, there are bonding forces which influence the chemical properties.
Internal molecular forces tend to be weaker (though not always!). They are the forces in
between molecules. For instance, between water molecules. They are non-bonding.
In high school, students probably learned about phase changes. But, you may not
remember sublimation. For instance, water subliming from the sun on the sidewalk, during
Endothermic process = takes heat to go from left hand side towards right hand side.
Energy is given off.
Favourite example: Florida orange trees are sprayed with water, to protect the fruit inside,
when it gets cold/freezing outside.
Liquids have very low compressibility.
If you contaminate pumps with an oil which vaporizes badly, with another that vaporizes
easily, causes many problems (creating gas pockets, for example).
The viscosity of gas is more so for gas than it is for liquid; we will learn about this more
Heats of vaporization are shown in the slide (see graph: Heats of vaporization and fusion
for several common substances).
Water is very high, and Argon is very low. Argon atoms don't stick together very strongly.
Metals like Mercury have so many electrons that they give rise to strong reactions, takes a
lot of heat to vaporize.
9 Jan 2012 CHM151Y1Y The Molecular Science LEC 101
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