Kinetic Molecular Theory

by Jules Bruno
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So remember the kinetic molecular theory is a way that we try to understand ideal gas laws if they did exist. Remember, ideal gas laws themselves are completely imaginary with the kinetic molecular theory, we have three postulates Postulate, one deals with the volume of these ideal gas molecules here, we're going to say under the first postulate, the size of the particle is significantly smaller and negligible, meaning not important. Well, compared to the volume of the container Here, we're going to say the volume of a gas particle itself represents less than .01% of the total volume of the container. So, a simple gas molecule particle doesn't take up very much space at all, so much in fact, that its volume is not important here. I'm showing the gas molecules in a larger format so we can better see them. But in actuality they're going to be incredibly incredibly small. Each one postulate to deals with temperature. We're going to say here under postulate too, as the temperature increases, we say, the molecules moving at higher velocities will also increase. Here we have the root mean square speed for three curves, three gasses and here we're going to say that each of these curves can be found at a different temperature. So let's say that this one here is at 330°C. We'd say that this one here is at 200°C. And let's say here that this one here is at 25°C. Actually let's make this 100 bigger differences in temperature, their differences in temperature will result in different overall speed or velocity for the gas molecules here. The root mean square speed is just under 1000 here Here, it's just between 400 and 600 and here, it's just over 400 m/s as the temperature is increasing for each of the curves, we see that their speed or velocity is higher. Finally, the final and third postulate deals with the forces of gasses here we say that the collision between gas particles and the walls of the container are completely elastic. If we were to imagine ideal gasses, now, what does it mean to be elastic? Well, that means that these ideal gas particles will behave as though they have no attractive or repulsive forces between the gas around them and the walls of the container. So, a good way to think about this is if you've ever watched ping pong balls within a container bouncing around, that's kind of an elastic collision, they're bouncing around, hitting the walls, hitting each other, but they're not sticking together, they're not pushing each other away, they're just moving around their own momentum, moving around, moving around. And that's what we talk about ideal gas laws, an ideal gas is behaving elastically. They may bump into each other, but there's no repulsive or attractive forces between those gas molecules. Right? So these are the three postulates that we use for us to better understand if ideal gas did exist. These are the behaviors that they would have.