the kinetic molecular theory l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
The Kinetic Molecular Theory PowerPoint Presentation
Download Presentation
The Kinetic Molecular Theory

Loading in 2 Seconds...

play fullscreen
1 / 23

The Kinetic Molecular Theory - PowerPoint PPT Presentation


  • 608 Views
  • Uploaded on

The Kinetic Molecular Theory. A model to explain the behavior of ideal gases The particles are small compared to the distances between the particles Assume that the volume of the individual particles is negligible. The Kinetic Molecular Theory. The particles are always moving.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'The Kinetic Molecular Theory' - Rita


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
the kinetic molecular theory
The Kinetic Molecular Theory
  • A model to explain the behavior of ideal gases
    • The particles are small compared to the distances between the particles
      • Assume that the volume of the individual particles is negligible
the kinetic molecular theory2
The Kinetic Molecular Theory
  • The particles are always moving.
    • Particles colliding against the walls of

the container result in the pressure exerted by the gas.

kinetic molecular theory
Kinetic Molecular Theory
  • The particles do not exert any force on each other; they neither attract nor repel each other.
  • The average kinetic energy of the gas particles is directly proportional to the Kelvin temperature of the gas
the kinetic molecular theory4
The Kinetic Molecular Theory
  • The true test of a model
    • The predictions based on the model should fit the experimental observations
the kinetic molecular theory5
The Kinetic Molecular Theory
  • Boyle’s Law
    • Decrease the volume, the gas particles will hit the wall more often
        • More collisions, more pressure
        • I.e., as the volume decreases, the pressure increases
the kinetic molecular theory6
The Kinetic Molecular Theory
  • Gay-Lussac’s Law
    • Increase the temperature, and the kinetic energy of the gas molecules will increase, their speed will increase, so the molecules will hit the wall with greater force and greater frequency
      • I.e, as the temperature increases, the pressure increases.
the kinetic molecular theory7
The Kinetic Molecular Theory
  • Charles’ Law
      • Increase the temperature, and the gas molecules will have greater kinetic energy, and thus, greater speed. The particles will hit the walls more often. To keep the pressure constant, the volume would have to increase to compensate for the increased speed.
      • I.e., At constant pressure, as temperature increases, the volume increases.
the kinetic molecular theory8
The Kinetic Molecular Theory
  • Avogadro’s Law
    • Increase the number of gas particles at a given temperature would result in more collisions, and thus more pressure. To keep the pressure constant, the volume would have to increase.
    • I.e., At some constant temperature and pressure, as the number of particles increase, the volume increases.
the kinetic molecular theory9
The Kinetic Molecular Theory
  • Dalton’s Law of Partial Pressures
    • Since all gas particles are independent of each other, it doesn’t matter what the identity of the individual particles are.
    • The sum of the pressures of the individual gases would give the total pressure.
the kinetic molecular theory10
The Kinetic Molecular Theory
  • The Meaning of Temperature
    • The Kelvin temperature indicates the average kinetic energy of gas particles
      • Two different gases at the same temperature will have the same average kinetic energy
      • From physics:
        • (KE)ave = 3/2 RT
        • This equation means, higher temperature, greater motion
real gases
Real Gases
  • No such thing as an ideal gas
  • Real gases begin to behave like ideal gases under ideal conditions.
    • at low pressures
    • At high temperatures
real gases12
Real Gases
  • Look at real gas behavior
    • Graph of PV/nRT vs P
    • For ideal gases, PV / nRT = 1 at any pressure
    • For real gases, PV / nRT approaches 1 at very low pressures (below 1 atm)
real gases13
Real Gases
  • What is the effect of temperature when plotting PV / nRT vs. P?
    • PV / nRT approaches 1 at low pressure and at high temperatures
real gases14
Real Gases
  • Johannes van Der Waals
    • Developed an equation for real gases
    • Received a Nobel prize for his work
ideal gases vs real gases
Volumeless

Do not interact with each other

Finite volumes

Particles do take up space

Volume of the gas is actually less than the volume of the container

Particles do attract each other

Ideal Gases vs. Real Gases
van der waals equation
van der Waals Equation
  • Correction factors for the ideal gas law
  • Correct for the volume:
    • The actual volume of a real gas is
      • V – nb
      • V = volume of the container
      • n = # moles of gas particles
      • b = constant, determined using experimental results
van der waals equation17
van der Waals Equation
  • Correction factors for the ideal gas law
  • Correct for the attractive forces between particles
    • Attractive forces would result in fewer, as well as slightly weaker collisions, resulting in less pressure.
van der waals equation18
van der Waals Equation
  • Pobs = observed pressure
  • P’ = pressure expected from the ideal

gas law

  • Pobs = P’ – correction factor
van der waals equation19
van der Waals Equation
  • The correction factor for the attractive forces would also have to be experimentally determined.
  • Depends on
    • concentration of gas molecules (moles/liter or n/V)
      • more gas molecules, more interactions
  • Correction factor: a(n/V)2
    • a = proportionality constant
van der waals equation20
van der Waals Equation
  • Pobs = nRT – a (n/V)2

V – nb

Rearrange to get van der Waals equation:

[Pobs + a(n/V)2] x (V – nb) = nRT

( Pcorrected. Vcorrected = nRT)

van der waals equation21
van der Waals Equation
  • A real gas becomes more like an ideal gas at low pressure…
    • Low pressure implies a large volume for the gas particles…the volume of the gas becomes the volume of the container as the gas particles (nb becomes very small) get farther apart
    • note that b is smaller when gas particles are smaller (b for He is 0.0237 L/mol while b for Xe is 0.0511 L/mol)
van der waals equation22
van der Waals Equation
  • A real gas becomes more like an ideal gas at high temperature…
  • High temperature means the gas particles have high kinetic energy and are moving past each other with greater speeds, giving the particles less of a chance to feel any attractive force. Pobs approaches Pideal
real gases and ideal gases
Real Gases and Ideal Gases
  • In summary, a real gas approaches the behavior of an ideal gas
    • at low pressure (large container)
    • at high temperature
    • when the gas experiences few attractive forces (the more nonpolar the particle, the weaker the attractive forces)