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Kinetic-Molecular
Theory
?Kinetic Molecular
Theory (KMT) is a
model used to
explain the behavior
of gases.

Major Ideas of Kinetic
Molecular Theory
?Gases contain particles
(usually molecules or
atoms) that are in
constant, random,
straight line motion.

Molecular Theory
?Gas particles collide with
each other and with the
walls of the container. The
collisions transfer energy,
but there is no net loss of
energy.

Molecular Theory
?Gas particles are
separated by relatively
great distances. Because
of this, the volume
occupied by the particles
themselves is negligible.

Molecular Theory
?Gas particles do not
attract each other.

The Nature of Gases
? KMT Theory explains why gases exert
pressure
? Not only do the gas particles collide with
each other, but they also collide with the
walls.

The Nature of Gases
? The collisions with the wall exert a force
over the surface area of the wall.
? That is they exert pressure on the
wall��
? Recall that pressure is a force per unit
area.

Units of Pressure
? We will use two different units for
pressure.
? Atmospheres (atm)
? kiloPascals
? Animation

Temperature
? Recall that temperature is the average
kinetic energy of the particles.
? So, the higher the temp, the faster the
particles are moving.

Behavior of Gases
? There are four variables��
? # of gas particles present
? Pressure
? Temperature
? Volume
? �� that explain the behavior of gases.

Boyle��s Law
? Boyle��s Law states that the volume of a
given amount of gas held at constant
temperature varies inversely with the
pressure.
? Mathematically��
P1V1 = P2V2

Chemistry Lab
Pressure-Temperature
Relationship in Gases

Gay-Lussac��s Law
? States that the pressure of a given
mass of gas varies directly with the
kelvin temperature when the volume
remains constant.
? Mathematically, ��
P1 / T1 = P2 / T2

Practice Problem
? A sealed rigid container has a volume of
2.5L, and a pressure of 2 atm at 400K.
What will be the new pressure if the
container is cooled to 300K?

Charles��s Law
? States that the volume of a given mass
of gas is directly proportional to to its
kelvin temperature at constant pressure.
? Mathematically, ��
V1 / T1 = V2 / T2

Combined Gas Law
Equation
? The relationships among pressure
temperature, and volume can be
mathematically represented by an
equation know as the combined gas
law��
P1V1 / T1 = P2V2 / T2
(reference tables)

Practice Problem
? What volume will a gas occupy if the
pressure on 300 cm3
of gas at 5.0 atm
is increased to 7.0 atm? Assume the
temperature remains constant.

Standard Temperature
and Pressure
? Standard pressure is defined as 1
atmosphere
? One atmosphere is equal to��
? 101.3 kPa
? 760 mm Hg
? 760 torr
? Standard temperature is defined as 00
C
(273 K)

Lets Practice More��
? If 120 cm3
of a gas is at STP, what
volume will the gas occupy if the
temperature is raised to 500
C and the
pressure is increased to 950 torr?

Ideal vs. Real Gases
? When gas laws are used to solve
problems, the results don��t always
agree exactly with lab results
? The explanation is that the assumptions
of KMT are not exactly correct.

? Gas particles really do attract one
another!
? In most cases, IMF��s are so small they can
be ignored
? But in extreme cases, the IMF��s become
significant and important
? For example, water becomes snow or rain
when the temps get low enough.

? Gas particles actually do occupy
volume!
? As pressure increases, the volume
occupied by the by the gas particles can��t
be ignored.
? At high pressures, there are more frequent
collisions.

Under What Conditions
Is A Gas Nearly Ideal?
? Low Pressure
? High Temperature
? Because those conditions allow the
molecules to stay far away from one
another.

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Kinetic molecular theory presentation 3 ESO

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Kinetic molecular theory presentation 3 ESO