Start typing, then use the up and down arrows to select an option from the list. ## General Chemistry

Learn the toughest concepts covered in Chemistry with step-by-step video tutorials and practice problems by world-class tutors

7. Gases

# Kinetic Molecular Theory

A gas is seen as a collection of molecules or individual atoms that are in constant motion. The Kinetic-Molecular Theory tries to use data of real gases to predict how an ideal gas would behave if they existed.

Examining the Kinetic-Molecular Theory
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concept

## Kinetic Molecular Theory 1m
Play a video:
Now, before we talk about the kinetic molecular theory, let's talk about an ideal gas. Now we did ideal gas law theory. We looked at different calculations. We looked at Stoke geometry deal dealing with ideal gas theory. But what we need to realize is that the ideal gas is an imaginary gas, and it acts as though it is alone by behaving independently of other gasses around it. Now, ideal gas is pretend as though they're the Onley gas within a container that they're not influenced by any other gasses around them. In reality, all containers have hundreds, thousands, maybe even millions of gas molecules moving around, bouncing into each other, affecting one another's trajectories. Some of them, if they hit hard enough and in the right spot, they can actually stick together. Now, if we're talking about ideal gasses and they're not riel, how can we talk about them? Well, the kinetic molecular theory. What it does is it uses data of riel gasses to predict how ideal gasses would behave if they existed. So even though ideal gas is air, not rial, we can actually look at riel gasses around us and predict their behavior. If they were around. All right, So now that we know the usefulness of the kinetic molecular theory, click on the next video and let's take a look at an example question.
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example

## Kinetic Molecular Theory Example 1 2m
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here. The example. Question says which conditions of pressure and temperature make for the most ideal gas. All right, so we just learned that ideal gasses are imaginary. But remember, if they did exist, how would they behave? Well, remember, we just said that an ideal gas acts as though it is alone inside of a container. So think about the conditions that foster this whole thing of being isolated being by yourself. So remember pressure. Think of it. Is this piston and outside pressure could push down on it. And here we have gas molecules and each one is far enough that they imagine themselves being alone. So think about it. Do we want pressure to be high or low? If pressure is high, this piston will get pushed down. And if that pushed piston got pushed down, the volume will get smaller. That would cause these gas molecules to come closer together, which they don't want. They wanna act as though they are alone. So we don't want high pressure. We want low pressure. So a is out next temperature. So let's just not worry about pressure. Now let's look a temperature. And here is my ugly flame. that I drew. Think about it when I'm adding he to a container. What happens to the volume? Remember, when we add heat to container, it will cause the volume to increase. We know this because of Charles law. With bigger volume, gasses can spread out be by themselves because there's nothing around them. So we want the temperature to be high, so we want low pressure, high temperature. This will foster a larger volume inside the container and allow these gasses to behave as though they are by themselves an independent of one another. So just remember, if you have a bit of trouble with this, just remember an ideal gas laws. Imaginary. It wants to be alone. Remembering the chemistry gas laws of Boyle's law, Charles Law of the Goggles Law also helps with our understanding on what helps to make a larger volume inside the container so these gasses could be by themselves
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concept

## Kinetic Molecular Theory 3m
Play a video:
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.
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Problem

Which of the following statements would correctly explain the non-ideal behavior of a gas based on the Kinetic Molecular Theory (KMT)?

a) At high temperatures the attractive forces between molecules becomes negligible.
b) At high pressure the volume of gas molecules become significant.
c) An increase or decrease in the moles of gas causes the gas constant value to change.

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Problem

Which of the following statements is/are true for gas molecules according to the Kinetic Molecular Theory?

I.Increasing the amount of gas molecules increases the pressure by increasing the force of the collisions.
II.Decreasing the temperature of a gas decreases the pressure by increasing the force of the collisions.
III.Decreasing the volume of a gas increases pressure by increasing the frequency of the collisions.

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Problem

Which statement is TRUE about kinetic molecular theory?

a) A single particle does not move in a straight line.
b) The size of the particle is large compared to the volume.
c) The collisions of particles with one another is completely elastic.
d) The average kinetic energy of a particle is not proportional to the temperature.

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Problem

Based on the kinetic-molecular theory, which of the following is/are true?
I.At a given temperature, all gases have the same average kinetic energy.
II.At a given temperature, different gases have the same average velocities.
III.The average kinetic energy is proportional to the absolute temperature. 