Kinetic Molecular Theory


This theory was developed to explain the gas behavior, hence called the "theory of moving molecules".

The theory of moving molecules helps us understand the following:

Application to Gas Laws

  1. As volume increases at constant temperature, the average kinetic of the gas (u) remains constant.
    However, as volume increases, gas molecules will have to travel further to hit the walls of the container.
    Therefore, pressure decreases.
  2. If temperature increases at constant volume, the average kinetic energy of the gas molecules (u) increases.
    Therefore, there are more collisions with the container walls and the pressure increases.

  3. The average kinetic energy (ε) is related to the root mean square speed (u) via the relation:
    ε = ½mu2
    Hence, as u increases, (ε) will also increase
    The average kinetic energy (ε) depends on the mass of the molecules (m) and their speed (u)
    Where the speed (u) is related to the molar mass of the gas molecule and the temperature through the relation:
    u =  3RT/M  Therefore, the speed of a gas molecule increases with temperature and decreases with its molar mass:

    Exercises on Kinetic Molecular Theory

    Exercise on Finding the RMS Speed of He atom

    Check your answers here: Solution to the Exercise on Finding the RMS Speed of He atom

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    Date of last modification: 2024