Phases of Matter and
Phase Changes
Unit 7
Chapter 13
Phases of Matter
Liquids and Solids
 Molecular
Level Comparison of Gases,
Liquids and Solids.
Liquid Properties
•Molecular Motion -Kinetic-molecular theory
predicts the constant motion of the liquid
particles
•Individual liquid molecules do not have fixed
positions in the liquid.
•Volume - Forces of attraction between liquid
particles limit their range of motion so that the
particles remain closely packed in a fixed
volume.
•Shape - Liquids can take the shape of their
container
Properties of Liquids

Density - Like gases, liquids can be
compressed. But the change in volume for
liquids is much smaller because liquid particles
are already tightly packed together.
•Diffusion - A liquid diffuses (mix) more
slowly than a gas at the same
temperature, however, because
intermolecular attractions interfere with the
flow.
Properties of Solids
•Exist in ordered patterns
Most solids have a crystalline shape
repeated over and over
Exception: Glass (considered an amorphous
solid, which means that the molecules are in
stuck in random positions
•Molecular Motion - Particles are in fixed
positions so they just vibrate in place.
•Diffusion - Cannot diffuse (cannot mix
spontaneously with other solids)
More Solid Properties
•Density - The particles in a solid are more
closely packed than those in a liquid.
 Solids
are usually the most dense of the
three states
Exception: Water
•Cannot be compressed – therefore they
have fixed volumes.
Changes In State
Solid
Freezing
Sublimation
Deposition
Melting
Vaporization
Liquid
Condensation
Gas
Exothermic vs. Endothermic

Exothermic Change – Heat Energy is released
to the surroundings.
 Molecules slow down, extra energy is
transferred to surrounding.
 Cooling phase changes are exothermic
•Endothermic Change – Heat energy is absorbed
by the system
-Molecules move faster as they absorb energy
-Phase changes that require energy (or heat) are
endothermic
Temperature oC
Heating & Cooling Curve
For a Pure Substance
Boiling/condensation
Temperature
Liquid and gas
Melting
Solid &
Liquid
Solid heating
Melting/Freezing
Temperature
Vaporization
Energy Added
Liquid heats
Gas
heats
Another graphic