Kinetic Theory of Gases PPT Physics Class 11

 Page 1


Kinetic Theory
Page 2


Kinetic Theory
In t r o d u c t io n
The behaviour of gases has fascinated scientists for centuries.
Early thinkers (Boyle, Newton, Dalton) explained gases as tiny moving particles.
Maxwell and Boltzmann developed the kinetic theory of gases in the 19th century.
In gases, interatomic forces are negligible as particles are far apart (unlike solids and liquids).
Kinetic theory successfully explains:
Pressure and temperature
Gas laws
Specific heats
Viscosity
Diffusion
All these phenomena connect to molecular motion.
Page 3


Kinetic Theory
In t r o d u c t io n
The behaviour of gases has fascinated scientists for centuries.
Early thinkers (Boyle, Newton, Dalton) explained gases as tiny moving particles.
Maxwell and Boltzmann developed the kinetic theory of gases in the 19th century.
In gases, interatomic forces are negligible as particles are far apart (unlike solids and liquids).
Kinetic theory successfully explains:
Pressure and temperature
Gas laws
Specific heats
Viscosity
Diffusion
All these phenomena connect to molecular motion.
Molecular Nature of Matter
Atomic Hypothesis
Richard Feynman famously highlighted 
the atomic hypothesis: "All things are 
made of atoms 4 tiny particles in 
constant motion, attracting each other 
at a distance and repelling when 
squeezed."
Historical Context
This idea, known since ancient times in 
India (Kanada's Vaiseshika philosophy) 
and Greece (Democritus), was 
scientifically formulated by John Dalton 
in the 19th century. Dalton's atomic 
theory explained how elements combine 
in definite ratios.
Modern Evidence
Modern evidence 4 like observations 
from electron microscopes 4 confirms 
that matter consists of molecules 
spaced at varying distances:
In solids, atoms are packed closely 
(around 2 Å apart).
In liquids, atoms are still close but 
free to move.
In gases, atoms are far apart with 
large mean free paths (thousands of 
Å).
This molecular picture explains 
properties like compressibility, flow, and 
dispersion in gases.
Page 4


Kinetic Theory
In t r o d u c t io n
The behaviour of gases has fascinated scientists for centuries.
Early thinkers (Boyle, Newton, Dalton) explained gases as tiny moving particles.
Maxwell and Boltzmann developed the kinetic theory of gases in the 19th century.
In gases, interatomic forces are negligible as particles are far apart (unlike solids and liquids).
Kinetic theory successfully explains:
Pressure and temperature
Gas laws
Specific heats
Viscosity
Diffusion
All these phenomena connect to molecular motion.
Molecular Nature of Matter
Atomic Hypothesis
Richard Feynman famously highlighted 
the atomic hypothesis: "All things are 
made of atoms 4 tiny particles in 
constant motion, attracting each other 
at a distance and repelling when 
squeezed."
Historical Context
This idea, known since ancient times in 
India (Kanada's Vaiseshika philosophy) 
and Greece (Democritus), was 
scientifically formulated by John Dalton 
in the 19th century. Dalton's atomic 
theory explained how elements combine 
in definite ratios.
Modern Evidence
Modern evidence 4 like observations 
from electron microscopes 4 confirms 
that matter consists of molecules 
spaced at varying distances:
In solids, atoms are packed closely 
(around 2 Å apart).
In liquids, atoms are still close but 
free to move.
In gases, atoms are far apart with 
large mean free paths (thousands of 
Å).
This molecular picture explains 
properties like compressibility, flow, and 
dispersion in gases.
Behaviour of Gases
Ideal Gas Approximation: Gases are simpler to 
study because the particles interact only when 
they collide. At low pressures and high 
temperatures, real gases approximate an ideal gas, 
satisfying: PV = KT. Where T is temperature in kelvin 
and K is a constant for the given gas.
Molecular Connection: Connecting this with the 
number of molecules:
K = NkB
kB is Boltzmann's constant.
Page 5


Kinetic Theory
In t r o d u c t io n
The behaviour of gases has fascinated scientists for centuries.
Early thinkers (Boyle, Newton, Dalton) explained gases as tiny moving particles.
Maxwell and Boltzmann developed the kinetic theory of gases in the 19th century.
In gases, interatomic forces are negligible as particles are far apart (unlike solids and liquids).
Kinetic theory successfully explains:
Pressure and temperature
Gas laws
Specific heats
Viscosity
Diffusion
All these phenomena connect to molecular motion.
Molecular Nature of Matter
Atomic Hypothesis
Richard Feynman famously highlighted 
the atomic hypothesis: "All things are 
made of atoms 4 tiny particles in 
constant motion, attracting each other 
at a distance and repelling when 
squeezed."
Historical Context
This idea, known since ancient times in 
India (Kanada's Vaiseshika philosophy) 
and Greece (Democritus), was 
scientifically formulated by John Dalton 
in the 19th century. Dalton's atomic 
theory explained how elements combine 
in definite ratios.
Modern Evidence
Modern evidence 4 like observations 
from electron microscopes 4 confirms 
that matter consists of molecules 
spaced at varying distances:
In solids, atoms are packed closely 
(around 2 Å apart).
In liquids, atoms are still close but 
free to move.
In gases, atoms are far apart with 
large mean free paths (thousands of 
Å).
This molecular picture explains 
properties like compressibility, flow, and 
dispersion in gases.
Behaviour of Gases
Ideal Gas Approximation: Gases are simpler to 
study because the particles interact only when 
they collide. At low pressures and high 
temperatures, real gases approximate an ideal gas, 
satisfying: PV = KT. Where T is temperature in kelvin 
and K is a constant for the given gas.
Molecular Connection: Connecting this with the 
number of molecules:
K = NkB
kB is Boltzmann's constant.
Avogadro's Hypothesis: This leads to Avogadro's hypothesis 4 equal volumes of gases at the same temperature and pressure contain 
the same number of molecules.
Ideal Gas Equation: The ideal gas equation: PV = ¿RT
¿ = number of moles
R = universal gas constant
T = absolute temperature
Dalton's Law: Dalton's law of partial pressures states that the total pressure of a gas mixture equals the sum of the partial pressures of 
its components.