Gaseous State SB

States of matter
Gaseous state

States of matter
1. Gaseous state
2. Liquid state
3. Solid and crystalline state
4. Liquid crystalline state

Gas general properties
• Gases can be expanded infinitively, therefore gases can fill containers
and take their volume and shape.
• Gases diffuse and mix evenly and rapidly.
• Gases have much lower densities than liquids and solids (There is a
lot of free space in a gas, therefore; It is the most compressible state
of matter).

Gas general properties
• Gas molecules travel in random paths and collide with one another
and with the walls of the container in which they are confined
• Hence, gas exerts a pressure (a force per unit area) expressed in
dynes/cm2, atmospheres or in mmHg (1 atm = 760 mmHg = 760
Torr).
• Gases have volumes that is expressed in liters or cubic centimeters
(1 cm3 = 1 mL).
• The temperature involved in the gas equations is expressed by the
absolute or Kelvin scale [0°C = 273.15 K (Kelvin)].

Ideal gas
• Ideal gas is a gas where no intermolecular interactions exist
and collisions are perfectly elastic, and thus no energy is
exchanged during collision.
• The properties of the ideal gas can be described by the
general ideal gas law, which are derived from Boyle, Charles
and Gay-Lussac laws

Ideal gas Boyle’s law
• Boyle’s law states that “the volume
and pressure of a given mass of gas
is inversely proportional”
• when the pressure of a gas
increases, its volume decreases
• P ∝ 1/v
• P =k/v
• P1V1 = P2V2
• P: pressure, K: constant,
• V: volume

Ideal gas Charles law
• Charles law states that “the
volume and absolute
temperature of a given mass of
gas at constant pressure are
directly proportional”
• when the temperature of a gas
increases, its volume increases as
well
• V ∝ T or V = k T
• V1/T1=V2/T2
• T: temperature in Kelvin

Ideal gas Gay-Lussac law
• The law of Gay-Lussac states that “the
pressure and absolute temperature of
a given mass of gas at constant
volume are directly proportional”
• when the temperature of a gas
increases, its pressure increases as
well
• P ∝ T or P = k T
• P1/T1 = P2/T2

Ideal gas Combined gas law
• Boyle, Gay-Lussac and Charles law can be combined to
obtain the equation
𝑷 𝟏 𝑽 𝟏
𝑻 𝟏
=
𝑷 𝟐 𝑽 𝟐
𝑻 𝟐
Where,
V = volume (dm3)
P= Pressure (atm.)
T= Temperature (K)

Combined gas law: Example 2
• A sample of methane CH4 has a volume of 7.0 dm3 at a temperature
of 4°C and a pressure of 0.848 atm. Calculate the volume of
methane at a temperature of 11°C and a pressure of 1.52 atm.

Ideal gas
General ideal gas law
• General ideal gas law (also called equation of state) relates the
specific conditions, that is, the pressure, volume, and temperature of
a given mass of gas.

Ideal gas
General ideal gas law: Molar gas constant
• The volume of 1 mole of an ideal gas under standard conditions of
temperature and pressure (i.e., at 0°C and 1 atm) has been found by
experiment to be 22.414 liters.
• Substituting this value in general ideal gas law:

Ideal gas
General ideal gas law: Molecular weight
• The approximate molecular weight of a gas can be determined by use
of the ideal gas law:
Where,
g= no. of grams of gas
M= molecular wt. of gas

Ideal gas
Kinetic Molecular Theory
1. Kinetic molecular theory explains the behavior of gases according to the
ideal gas law:
2. Gases are composed of particles called atoms or molecules, the total
volume of which is very small (negligible) in relation to the volume of
the space in which the molecules are confined.
3. Gas molecules exert neither attractive nor repulsive forces on one
another.
4. The particles exhibit continuous random motion. The average kinetic
energy, E, is directly proportional to the absolute temperature of the gas,
E =
𝟑
𝟐
RT.
5. The molecules exhibit perfect elasticity; there is no net loss of speed or
transfer of energy after they collide with one another and with the walls of
the confining vessel.

Real gas
• Real gases do not interact without energy exchange, and therefore do
not follow the laws of Boyle, Charles, and Gay-Lussac.
• Real gases olecules are not composed of infinitely small and perfectly
elastic non-attracting spheres.
• They are composed of molecules of a finite volume that tend to
attract one another.
• The significant molecular volume and the intermolecular attractions
between gas molecules affect both the volume and the pressure of
the real gas, respectively.

Real Gas
• Van der Waals Equation: The influence of non-ideal behavior of gas is
greater when the gas is compressed (At high pressure and low
temperature).
• Pressure correction: Real pressure = Ideal pressure + inward pull
• Volume correction: Real volume = Ideal volume – volume occupied by
gas molecules

Real Gas
• Van der Waals Equation: The van der Waals equation is a modified
ideal gas equation that considers the factors that affect the volume
and pressure of a real gas.
• The term a/V2 accounts for the internal pressure per mole resulting
from the intermolecular forces of attraction between the molecules;
b accounts for the excluded volume, which is about four times the
molecular volume.

References
• Sinko, P. J. M. A. N. 2006. Martin's physical pharmacy and
pharmaceutical sciences

Gaseous State SB

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