THE KINETIC THEORY
OF MATTER
The Kinetic theory has three basic
assumptions:
1. All matter is composed of
small particles (molecules,
atoms, and ions).
2. The particles are in
constant, random motion.
3. The particles are
colliding with each
other and the wall of
their container.
Kinetic theory helps explain the process of
dissolving.
Here is an example: Suppose a crystalline
substance like sugar is dissolved in water.
•Dissolving is a physical change, not a
chemical change, because the sugar still has
the same chemical formula!
•When a crystal dissolves, the molecules at
the surface of the crystal enter the
solution first because they are the ones
that are in contact with the moving water
molecules. Water molecules can “kick” the
sugar molecules from the surface of a sugar
crystal.
Though there are several ways to
increase the rate at which a solute
dissolves in a solvent, they all involve
increasing the number of particle
collisions.
•One way to increase the number of particle
collisions is to break or crush the solute into
very small particles. This increases the surface
area of the solute. More surface area means
more collisions between solvent and solute
particles.
Another way to increase the rate of dissolution is
to increase the kinetic energy of the solvent by
increasing the temperature. Increasing the
temperature of the solvent makes the molecules or
atoms of the solvent move faster. Faster solvent
molecules hit solute particles more often. This has
the effect of increasing the rate of dissolution
( Dissolution means dissolving ).
SUMMARY: If you want to dissolve something faster:
A.Add more kinetic energy by warming up the
solvent. This increases the number of particle
collisions and speeds up dissolving.
B. Crush the solute into smaller particles. This
increases the number of particle collisions by
increase surface area and this speeds up dissolving
C. Add more kinetic energy by agitating the solution.
This increases the number of particle collisions.
What is the difference between a dilute solution, a
concentrated solution, and a saturated solution?
Dilute: Few solute molecules compared to the
number of solvent particles. Lots of spaces between
the solvent molecules for more solute to be added.
What is the difference between a dilute solution, a
concentrated solution, and a saturated solution?
Concentrated: Many solute molecules compared to
the number of solvent particles. Less of space
between the solvent molecules for more solute to be
added.
What is the difference between a dilute solution, a
concentrated solution, and a saturated solution?
Saturated: Solute molecules fill ALL spaces between
solvent particles. No room left between the solvent
molecules. If any more solute is added it will settle
to the bottom and not dissolve.
What's the Difference between "Dissolving"
and "Melting"?
When a solid dissolves into a solvent, it does not
melt since no heat has to be added. It does not
change phase, but simply gets broken apart into
invisible molecules or atoms that are mixed into
the solvent.
In order to melt a solid, heat must be added to
raise its temperature above its melting point. No
other substance is involved.
A LITTLE QUIZ…
1. What is the theory that states “ Matter is composed of
particles that are in constant random motion”?
2. Suppose 50g of salt is dissolved in 200ml of water. In this
solution, what is the solvent? The solute?
3. Dissolution means ___________.
4. List three ways the rate of dissolution can be increased.
5 Identify each of the following as representative of a Dilute,
saturated, or concentrated solution.
6. So…was the wicked witch melting or dissolving?
A
C
B