PS – Change of State
IPC – Mr. Coburn
Introduction
Kinetic Molecular Theory is a fundamental theory of matter that explains physical properties in terms of the motion of
atoms and molecules. In kinetic theory, the thermodynamic behavior of matter (especially the relationships among
pressure, volume, and temperature in gases) is based on the dependence of the kinetic energy of the rapidly moving
particles of a substance.
Phases of Matter
Temperature is the term used to describe the average kinetic energy of particles in the substance. The higher the
temperature, the greater the particle motion. States of matter are dependent on the relationship between the
intermolecular attractive forces and kinetic energy in a substance.

Solid - Molecules are held close to each other by their attractions of charge. The molecules have an ordered
arrangement.

Liquid - Molecules will flow or glide over one another, but stay toward the bottom of the container. Motion is a bit
more random than that of a solid. They have enough kinetic energy to slip out of the ordered arrangement of a
solid.

Gas - Molecules are in continual straight-line motion. The kinetic energy of the molecule is greater than the
attractive force between them, thus they are much farther apart and move freely of each other.
Change of State
Change of State (phase change) occurs when thermal energy is added or removed from matter. Recall that states of
matter are dependent on the relationship between the intermolecular attractive forces and kinetic energy in a substance.
Greater thermal energy increases kinetic energy, which decreases the intermolecular attractive forces between particles
in a substance.
Complete the diagram below.
The graph at right was drawn from data
collected as a substance was heated at
a constant rate. Use the graph to answer
the following questions.
At point A, the beginning of observations, the
substance exists in a solid state. Material in this
phase has _______________ volume and
_____________ shape. With each passing
minute, _____________ is added to the
substance. This causes the molecules of the
substance to ____________ more rapidly,
which we detect by a ________________ rise
in the substance. At point B, the temperature
of the substance is ______°C. The solid begins
to __________. At point C, the substance is completely ____________ or in a ___________ state. Material
in this phase has _______________ volume and _____________ shape. The energy put to the substance
between minutes 5 and 9 was used to convert the substance from a ___________ to a ___________. This
thermal energy is called the latent heat of fusion.
Between 9 and 13 minutes, the added energy increases the ______________ of the substance. During the
time from point D to point E, the liquid is ___________. By point E, the substance is completely in the
__________ phase. Material in this phase has _____________ volume and ___________ shape. The energy
put to the substance between minutes 13 and 18 converted the substance from a ___________ to a
___________ state. This thermal energy is called the latent heat of vaporization. Beyond point E, the
substance is still in the ______________ phase, but the molecules are moving _______________ as indicated
by the increasing temperature.
Substance
Melting point
Boiling point
Which of these three substances was likely used in
Bolognium
20 °C
100 °C
this phase change experiment?
Unobtainium
40 °C
140 °C
Foosium
70 °C
140 °C
BONUS: For water, the value for the latent heat of vaporization is 6.8 times greater than the latent heat of
fusion. Imagine we were adding heat at a constant rate to a block of ice in a beaker on a hot plate, and it took 4
minutes for the ice to melt completely. How long would it take, after the water started boiling, for the beaker to
be completely empty (the liquid water totally converted to water vapor)?