Kinetic Molecular Theory and States of Matter in Physical Pharmacy

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S
TATES
 
OF
M
ATTER
 
Lecture 2
Assistant prof Dr. Fouadalssady
Physical pharmacy
 
K
INETIC
 
MOLECULAR
 
THEORY
( 
DEVELOPED
 
TO
SUPPORT
 
TO
 
THE
 
VALIDITY
 
OF
 
GAS
 
LAW
)
 
1.
Gases are composed of particles in constant
random motion .
2.
Because the size of the gas particles is so small ,
and the distance separating them is so great,
the volume occupied by the gas particles will be
negligible when compared to the volume of their
container.
3.
No appreciable intermolecular forces occur
except during collisions.
4.
All collisions are perfectly elastic . Kinetic
energy is conserved when gas particles collide
among themselves, or with the walls of the
container.
 
 
5.
The average kinetic energy of gas particles is
directly proportional to their absolute
temperature. All gases at the same temperature
have the same kinetic energy.
 
 
T
HE
 
LIQUID
 
STATE
 
Liquefaction of gases
When gas is cooled , it loses some of its kinetic
energy in the form of heat , and the velocity of
the molecules decreases .
If pressure is applied to the gas , the molecules
are brought within the sphere of the vander
waals interaction forces and pass into the liquid
state .
The transition from gas to a liquid and from a
liquid to a solid depend not  
only on the
temperature but also on the pressure
.
 
If the temperature is elevated sufficiently , a
value is reached above which it is impossible to
liquefy  a gas irrespective of the pressure applied
.this temperature , above which a liquid no
longer exist , is known as the 
critical
temperature
.
The pressure required to liquefy a gas at its
critical temperature is 
the critical pressure.
The further the gas is cooled below its critical
pressure, the less pressure is required to liquefy
it.
The critical temperature of water is 374°C or
647K ,and its critical pressure is 218 atm
whereas for helium are 5.2 K and 2.26atm.
 
The critical temperature serves as a rough
measure of the attractive forces between
molecules because at temperature above the
critical value , the molecules possess sufficient
kinetic energy so no amount of pressure can
bring them within the range of attractive
forces that cause the atoms or molecules to
stick together.
The high critical value of water results from
the strong dipolar forces between molecule and
particularly the hydrogen bonding that exist,
conversely only london forces  attracts helium
molecules.
 
A
e
r
o
s
o
l
s
Gases can be liquefied under high pressures in a
closed chamber as long as the chamber is
maintained below the critical temperature. When
the pressure is reduced, the molecules expand
and the liquid reverts to a gas.
 
This reversible change of state is the basic
principle involved in the preparation of
pharmaceutical aerosols.
 
In such products, a drug is dissolved or
suspended in a propellant, a material that is
liquid under the pressure conditions existing
inside the container but that forms a gas
under normal atmospheric conditions. The
container is so designed that, by depressing a
valve, some of the drug–propellant mixture is
expelled owing to the excess pressure inside
the container. If the drug is nonvolatile, it
forms a fine spray as it leaves the valve orifice;
at the same time, the liquid propellant
vaporizes off.
 
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The lecture by Assistant Prof. Dr. Fouadalssady in physical pharmacy delves into the Kinetic Molecular Theory, elucidating how gases consist of particles in constant motion with negligible volume. It explains the relationship between kinetic energy, temperature, and the transition from gas to liquid states. Additionally, it touches upon critical temperatures and pressures in liquefying gases, showcasing the differences between water and helium in molecular forces.


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  1. STATES OF MATTER Lecture 2 Assistant prof Dr. Fouadalssady Physical pharmacy

  2. KINETIC MOLECULAR THEORY( DEVELOPED TO SUPPORT TO THE VALIDITY OF GAS LAW) Gases are composed of particles in constant random motion . Because the size of the gas particles is so small , and the distance separating them is so great, the volume occupied by the gas particles will be negligible when compared to the volume of their container. No appreciable intermolecular forces occur except during collisions. All collisions are perfectly elastic . Kinetic energy is conserved when gas particles collide among themselves, or with the walls of the container. 1. 2. 3. 4.

  3. The average kinetic energy of gas particles is directly proportional to their absolute temperature. All gases at the same temperature have the same kinetic energy. 5.

  4. THE LIQUID STATE Liquefaction of gases When gas is cooled , it loses some of its kinetic energy in the form of heat , and the velocity of the molecules decreases . If pressure is applied to the gas , the molecules are brought within the sphere of the vander waals interaction forces and pass into the liquid state . The transition from gas to a liquid and from a liquid to a solid depend not only on the temperature but also on the pressure.

  5. If the temperature is elevated sufficiently , a value is reached above which it is impossible to liquefy a gas irrespective of the pressure applied .this temperature , above which a liquid no longer exist , is known temperature. The pressure required to liquefy a gas at its critical temperature is the critical pressure. The further the gas is cooled below its critical pressure, the less pressure is required to liquefy it. The critical temperature of water is 374 C or 647K ,and its critical pressure is 218 atm whereas for helium are 5.2 K and 2.26atm. as the critical

  6. The critical temperature serves as a rough measure of the attractive molecules because at temperature above the critical value , the molecules possess sufficient kinetic energy so no amount of pressure can bring them within the range of attractive forces that cause the atoms or molecules to stick together. The high critical value of water results from the strong dipolar forces between molecule and particularly the hydrogen bonding that exist, conversely only london forces attracts helium molecules. forces between

  7. Aerosols Gases can be liquefied under high pressures in a closed chamber as long as the chamber is maintained below the critical temperature. When the pressure is reduced, the molecules expand and the liquid reverts to a gas. This reversible change of state is the basic principle involved in pharmaceutical aerosols. the preparation of

  8. In such products, a drug is dissolved or suspended in a propellant, a material that is liquid under the pressure conditions existing inside the container but that forms a gas under normal atmospheric conditions. The container is so designed that, by depressing a valve, some of the drug propellant mixture is expelled owing to the excess pressure inside the container. If the drug is nonvolatile, it forms a fine spray as it leaves the valve orifice; at the same time, vaporizes off. the liquid propellant

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