Wize University Chemistry Textbook > Gases and their Properties
Kinetic Molecular Theory of Gases
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Kinetic Molecular Theory (KMT)
This theory describes the behaviour of ideal gases.
In normal conditions we can apply this to real gases as well...(more on the conditions required for this later)
The KMT operates under the following assumptions/simplifications:
Wize Concept
- Ideal gases are in constant, random motion and move in straight lines
- The size of gas particles is negligible compared to the distance between particles. As a result of this, the volume of gas particles is considered to be 0.
- There is constant motion of particles and collisions of gas particles (with other gas particles and with the walls of the container) are completely elastic so that the total kinetic energy is conserved before and after a collision.
- There are no intermolecular forces between gas particles (they don't attract or repel each other).
- Temperature is directly proportional to the average kinetic energy of the gas particles.
- If we increase temperature, do you think the gas molecules would collide with container walls more/less often?Moreoften.
- And with an increase in temperature would the gas particles collide at slower or greater speeds?Greaterspeeds
Watch Out!
T should always be in Kelvins (K) for chemistry calculations :)
T(in K) = T(in °C) + 273
Wize Tip
You can just assume we are dealing with an ideal gas unless stated otherwise in a particular exam question!
Note: to measure pressure( P=F/A), we need to take into consideration the number of collisions and force of those collisions between gas particles and the walls of the container
This can help us understand WHY the KMT says what it does for IDEAL gases:
- If gas particles had volume they would be quite large and would have more/less:moreintermolecular forces/attractions to one another. This would mean that they would interact with the walls of the container more/less:lessand result in a decrease/increase:decreasein pressure.
- If collisions weren't elastic, then over time gas particles would hit the walls of the container with more/less:lessforce and increase/decrease:decreasethe pressure.
- We will explain this concept more when we look at real vs ideal gases!
The KMT for ideal gases helps to keep conditions in the container stable!