The Kinetic Molecular Theory of Gas (part 1)

This is the first lesson of our unit on gases. Let's start this unit with a quick review on phase changes of

kinetic

energy and states of matter. This information may sound familiar to you, but even if it is, I think it will still be familiar. a useful review, then let's talk about a

theory

with a really scary name, the

kinetic

molecular

theory

of gases, which is a lot scarier than it looks and gives us some rules for how we can think about gases and, finally, Look at some unique properties of gases that are very different from those of solids or liquids, so let's take a look at kinetic energy, first of all, kinetic energy is a type of energy that anything has if it moves, for what a Mack truck does if it hurtles down. the road has kinetic energy and even a small moving atom has kinetic energy.

Think about kinetic energy: the faster something moves, the more kinetic energy it has, so children running down the street have more kinetic energy than the same child simply walking down the street. In the same way, an atom that moves very fast has more kinetic energy than that same atom that moves very slowly. The idea of ​​kinetic energy is

part

icularly important when we start talking about the phases of matter. Let's do a quick refresher to review what we probably already know. phases of matter I have indicated here some specific representations of the phases of matter. I have a container and some

part

icles in it.

I have a representation of a solid, a liquid and a gas. Let's start with a solid, a solid here like all the other phases. Matter is made up of particles, that is what these small red circles represent. Particles can be atoms or they can be molecules that are formed when atoms join together in any direction. All things are matter and all things are made of particles, so in a Solid, the particles, as you can see, are very close together, have very little kinetic energy, they move a little bit, but for the most part they are locked together. in place and are locked to their neighbors, particles in liquid have They move with more kinetic energy and are freer to move.

They are still cooped up with their neighbors to some extent, but they swim. They swim near the particles. The nearby gas is on the other side. In fact, I have a ton of kinetic energy to make this image even more accurate. What I'm going to do is add some arrows. These arrows will represent the fact that these gas particles are in constant motion. They are moving all over the place, colliding with each other and hitting the sides of the container. In fact, these gas particles move so fast that at room temperature they have an average speed of one thousand. miles per hour, that's how fast they move around here in this container, so the solids, liquids and gases have increasing amounts of kinetic energy.

Gases have the most kinetic energy, they fly there and are not connected to their Neighbors at all, this is a very superficial representation of what a gas looks like, but often we will want to break down the issues and think about the gas conceptually in a way. Obviously we cannot see how these gas particles behave, so in the problems that we are going to solve later we have to have a way of thinking about it, a way of conceptualize it, so it is useful to establish a series of rules. To know how we expect gases to behave well, let's make these rules or assumptions and then we can take them into account when we have to solve problems or do calculations.

This list of rules is what is called the kinetic

molecular

theory of gases, it is often simply known as the kinetic theory of gases and, as I said, it is a list of rules, expectations, assumptions of how we expect things to behave. gases Now, if a gas follows each of these rules, we call it an ideal gas, but in the real world it is very difficult to achieve. With an example of something that always follows all the rules, we might think that there are some things like a perfect student, an ideal student or an ideal child, but that is rarely the case, we almost always find some exceptions to the rules and so on because That's useful to think about an ideal gas, but in the real world none of these gases we're going to talk about follow all the rules all the time.

At the end of this unit we will look at some particularly bad offenders. gases that break the rules more often than others and we will look at certain situations that cause the gases to break the rules the most, although when we look at all the gases that we are going to look at now, we will assume that their ideal gases we will assume that they follow all rules all the time and for the most part most of these gases only break the rules in small pieces from time to time, so we can safely assume that all the gases were trading.

Let's follow these rules of kinetic molecular theory, like this Let's take a look at some of the rules of this and again, sometimes it's just known as kinetic theory. I want to write here the molecular kinetic theory of gases, so in no particular. In order, let's take a look at some of the assumptions we make about gases, so here's the first one. Gases consist of very small particles that are widely spaced relative to their size. This is something that is very difficult to represent visually and I certainly didn't do it. good job on the phase and phase diagrams i just showed you gas particles in the picture i drew look like the size of marbles in a glass jar this is not true at all gas particles are so small that instead of Think of them like marbles and glass jars, if the gas particles are the size of marbles, our container would be the size of a football stadium, so these guys are absolutely tiny and there is a ton of empty space between them, that's The first thing we want to keep in mind when we deal with gases here is the second thing and this is very important.

Gas particles are in constant random motion. We hinted at it earlier with the arrows I drew. The gas is moving. The moving particles are constantly colliding with each other and with the walls of the container, so whenever I have gas in any type of container or even if it's just in a room, these guys are spinning around, bouncing off the walls, and they're bouncing around a few times. against others Now let's think a little more about those equilibria there are a variety of ways that things bounce off each other and here we say that collisions between gas particles and the walls of containers are elastic collisions what is an elastic collision? about two slime balls, these two slime balls on either side of me come together and what's going to happen, they're just going to hit each other on the girl.

This is what we call an inelastic collision, which means that the kinetic energy that both of these guys had wasted in the collision, they were both moving, they got together and they just went around and all the kinetic energy to accelerate the motion that They had disappeared in the collision. This is like what happens if you drop an egg. against the side of a wall, it hits the wall and then just drips, but the motion it had, the kinetic energy, disappears, it is an inelastic collision, the collision between gas particles and the walls of the container, on the other hand, are collisions elastic, a good way of thinking.

About an elastic collision is to think about what happens when red or pink round rubber balls hit each other, they hit and bounce or one of those pink rubber balls hits the side of a wall BAM, it bounces back, the energy kinetic energy is not wasted in the collision, this ball hits here and has the same amount of kinetic energy afterwards as it had when it started. That's the exact type of collision where gas particles enter, collide with each other, and simply separate or collide. the side of the wall of a container and they just bounce off it, so when you think about gas particles colliding, you always have to keep in mind the idea of ​​elastic collisions.

Furthermore, we can say that there are no forces of attraction or repulsion between them. gas particles some particles, such as water molecules, resemble each other and therefore, almost like small weak magnets, they tend to attract other particles towards particles that have the same charge, they do not like each other, they have afraid of each other, so they will repel each other they don't want to get close to each other what this loss means when we say that there are no forces of attraction or repulsion between the gas particles what we mean is that the gases are flying and they are not going to start grouping together because they attract each other, that does not happen, there is no such attraction, in the same way, suppose two gas particles pass each other, they will just fly by if they repel each other soon, they would.

They hit each other that way when they get close, that doesn't happen, they don't repel each other and they don't attract each other either. Lastly, this is what I think is probably the most important thing to keep in mind when we talk about the kinetic theory of gases and that is that the average kinetic energy of the gas particles depends on the temperature of the gas, the more The hotter it is, the faster they move, so remember that hotter the gas equals faster motion. This is tremendously important, the hotter it is, the faster these will be.

Gas particles move, so in this kinetic theory of gases we have looked at some of the rules that we always want to keep in mind when dealing with gases and again we are going to assume that all the gases that we use. We're dealing with following these five rules that we just talked about.