Kinetic Theory
and
Exothermic/Endothermic
Reactions
Kinetic
Theory
Kinetic Theory - A theory
concerning the
thermodynamic behavior of
matter, especially the
relationships among
pressure, volume, and
temperature in gases.
It is based on the
dependence of
temperature on the kinetic
energy of the rapidly
moving particles of a
substance.
According to the theory, energy
and momentum are conserved in
all collisions between particles,
and the average behavior of the
particles can be deduced by
statistical analysis.
Kinetic Theory of Matter
1) All matter is made up of atoms and
molecules that act as tiny particles.
2) These tiny particles are always in
motion.
1) State of matter depends on its molecular
motion as measured by temperature
• ↑ temperature = ↑ motion of particles
• ↓ temperature = ↓ motion of particles
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Kinetic Theory of Matter
3)
At the same
temperature, the heavier
particles move slower
than the lighter particles.
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Temperature
•A measure of the
average kinetic energy
(K.E.) in a sample.
•K.E. – Energy of
Motion
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Absolute Zero
• Temperature at which all
molecular (particle) motion
stops.
• 0 Kelvin ( -273 °C; -459 °F)
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Intermolecular Forces (IF’s)
• Force of attraction between molecules/particles.
• Become stronger as molecules get closer together;
therefore IF’s are strongest in solids.
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3 States of Matter
- Solid
- Liquid
- Gas
Basis for classification of
the 3 States of Matter
- Particle arrangement
- Energy of the Particle
- Distance between particles
Solids
The particles in the solid
vibrate around a fixed
point.
Most solids are
crystalline—they have
definite repeating structure.
Solids are held
together by strong
intermolecular (IM)
forces.
Substances that have more
than one crystalline structure
are called allotropes.
Carbon can have several
allotropes, for example
diamonds and coal.
Amorphous
solids (like glass)
don’t have a
definite structure
Melting point is the
temperature at which a solid
becomes a liquid.
As the particles gain kinetic
energy, they vibrate and spin
themselves right out of their
structure.
Freezing point is the
temperature at which a liquid
becomes a solid.
As the particles lose kinetic
energy, the intermolecular
forces hold the particles
together.
The melting point
and freezing point of
any substance is at
the same
temperature!!
Liquids
In a liquid, particles vibrate and
spin as they move from place to
place and slide past one another.
There are still intermolecular
forces holding them together,
just not as strong as those of a
solid.
Both liquids and gases can flow, but liquids
have viscosity.
Viscosity is a liquid’s resistance to flow.
Syrup has a high viscosity (it is difficult to
pour.) Water has a low viscosity.
There are two ways in
which a liquid becomes a
gas:
Evaporation and Boiling
Evaporation — the particles
with the highest amount of
kinetic energy go from liquid
to gas.
This is a cooling process,
because it lowers the overall
Kinetic Energy of the liquid.
Evaporation is the reason why
sweat cools your body.
The evaporation of a liquid
only occurs at the surface of
the liquid.
The boiling point is the point at which
the internal vapor pressure of a liquid
is equal to the external pressure. (It is
also a cooling process).
Boiling occurs throughout the liquid
The boiling point is a function of
BOTH temperature AND pressure.
Gases
A gas is composed of
particles that are small,
hard spheres with almost
no volume or particle
interaction.
Gases
Particles in a gas are in
constant motion—they travel
straight paths unless they
collide with another particle
or their container.
Gases
All collisions are
considered
elastic—no
energy is lost
Gases have the highest kinetic
energy.
Gases have the weakest
intermolecular forces.
In a gas particles move very
quickly and independently of each
other.
Gas Pressure
Kinetic theory explains
the existence of gas
pressure, the force
exerted by a gas per unit
surface area.
Gas Pressure
The force of one molecule
hitting an object is relatively
small, but the result of
billions of particles of air
hitting a surface at once is
significant.
The absence of particles is
called a vacuum.
No particles = no pressure
Atmospheric pressure is the
amount of pressure from the
particles in the atmosphere
colliding with objects.
Atmospheric Pressure
decreases with altitude
because the number of air
particles decreases with
altitude.
Temperature
When a substance is heated, the
particles speed up, causing
faster movement and more
collisions.
This is a rise in temperature.
Which phase of matter
(ice or steam) do you
think has the most kinetic
energy?
The least?
Exothermic
and
Endothermic
Reactions
An exothermic reaction is a
chemical reaction that releases
energy in the form of heat.
Feels HOT.
Expressed in a chemical equation:
reactants → products + energy
Example
mixing water and strong
acids
An endothermic reaction is a
chemical reaction that requires heat
energy in order for the reaction to
occur.
Feels COLD
Expressed in a chemical equation:
reactants + energy → products
Example
evaporation of water
On the following diagram,
determine which line
represent a exothermic
reaction and which line
represent an endothermic
reaction.
Use your notes to complete the
‘Kinetic Theory and ExothermicEndothermic Practice Sheet’ found
on LMS.
10 pts. on weekly grade
Work on for the remainder of class.
Due Monday