01:160:161 Lecture 2: Chapter 12 – phase changes and lattice structures

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8 Feb 2017
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Chemistry Eshana Bethur
Chapter 12 Intermolecular Forces and Phase Changes
All matter exists in three different states, and in all three phases, electrostatic forces among the
particles, called intermolecular forces, combine with the particles’ kinetic energy to create
properties of the phases, like phase changes.
o An Overview of Physical States and Phase Changes
Intramolecular forces are bonds within molecules between atoms
Intermolecular forces are forces of attraction between molecules
Kinetic-molecular view of the three states
The state of matter depends on the intermolecular interactions of particles
In a gas the molecules have a lot of kinetic energy and their attractive energy are too
small
In a liquid the attractions are stronger than they are in a gas, there is very little free
space between particles, liquids resist an external force
In a solid the attractions are stronger than they are in both a gas or a liquid, it does not
flow and it has a fixed shape
Types of Phase Changes
For each phase change, an element
has a standard enthalpy change per mole
Heat of Vaporization (Hvap)
Heat of Formation (Hfus )
Condensing and freezing are
exothermic changes
Melting and vaporizing are
endothermic changes
o Quantitative Aspects of Phase Changes
Heat Involved in Phase changes: A Kinetic Molecular Approach
Use a heating curve to show how the phase changes occur
Melting point heat of fusion (moles heat of fusion)
Boiling point heat of vaporization (moles heat of vaporization)
For the states of matter use the equation q = mcT
The Equilibrium Nature of Phase Changes
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