Hi chemists, this is Ms. Raz and we are going to start our unit on states of matter. In this video, we are going to primarily focus on kinetic molecular theory of gases, or sometimes called kinetic theory, which is sometimes abbreviated KMT. At the end of this video, you should be able to describe the basic principles of kinetic theory of gases and explain where gas pressure comes from and what affects it.
You probably remember that kinetic energy is really energy of motion, so the word kinetic means motion. And the kinetic theory of matter says that all particles of matter are in constant motion. Now, you may think of solids in that the particles aren't moving very much, and that is true, but they are still moving, even though it's hard for us to see. The word gas comes from the Greek word meaning chaos, and if you look on the right-hand side here you can see this is kind of what gases look like on the particulate, where these particles can collide with each other and the walls of the container.
Now scientists have engaged in many, many experiments that have led to evidence that suggests the following behaviors of gases. So we are going to focus on individual theories associated with the kinetic theory of gases. The first one is that gases are made up of tiny particles of negligible volume.
So basically the word negligible means really small or insignificant volume. Gas particles are usually very far apart, therefore they do not attract or repel each other. However, there is an attractive force between the particles of solids and liquids. So we as scientists assume that there are really no attractive forces between those particles. Particles move independently of each other, and that's why gases will expand to fill their container.
The word diffuse means to move out, so a way to describe gas particle motion is we say they diffuse. Gases also have no definite volume. Gas particles will also move incredibly fast, so thousands of kilometers an hour.
And you know this if somebody shows up at your door with a pizza, you can, if you're on the other side of the room, you smell it immediately. Another example is if somebody's cleaning in your household, right? When you open a bottle of ammonia, the entire room will eventually smell. And really the reason why is because these particles, just like you saw in the video clip over there, is that these particles are moving randomly in straight lines until they collide with each other or the objects in the room. We describe gas particle motion as a random walk, basically where gas particles will move in a straight line until they collide with another particle and then change direction.
And then, of course, this repeats. This is a really quick video clip of hydrochloric acid forming ammonium chloride. So you can see the HCl in the flask is combining with the ammonia on the tip of the Q-tip. And so that white solid that you see formed there, that is the ammonium chloride. So that is giving evidence to the fact that our gas particles are moving in kind of a random walk type motion.
We also assume that any collisions between gas particles are elastic, which means that these gas particles will essentially hit and then break apart from each other. They do not stick together. Kinetic energy at this time can be transferred, but it's never lost. Gas pressure is a measure of collisions of gas particles with each other and the walls of the container.
As the number of collisions increases, the pressure will increase. And you may say, Ms. Raz, why do you have popcorn popping in the lower right-hand corner? Well, basically, kernels have water inside them. And when you put them in the microwave, that water will vaporize and essentially cause that popcorn kernel to pop inside out. You will see more collisions result if there are more particles in a particular space and if you increase the temperature.
So if you increase temperature, the pressure will increase because those particles have more kinetic energy and therefore they're colliding with each other more and the walls of their container more frequently. So that is definitely going to increase pressure. Another way to show gas pressure is by using peeps in a vacuum. So where there is no gas pressure, that is called a vacuum. It's just a region of empty space.
And gas pressure is equal to zero, so there must be no collisions. So with peeps, here's an example of a video. Okay, so we have our two bunnies here.
Pierre will be the stunt bunny, he is the bunny inside, and Marie is the bunny outside, so we can look at the size difference between them. Oh, Pierre, I don't know, this could be dangerous. Don't worry, Marie.
We'll be alright Start the vacuum pump What is going on right now? It's coming up It's making that pumping sound Up here! Something is happening to you!
I feel so funny! Oh, Pierre is getting really big! Oh boy! That kid's mom is still sucking air out! But we're great, we can't even vacuum in there!
All the little tiny bubbles in the marshmallow are expanding! So you can see in that demonstration that basically the teacher was removing any air pressure and air pressure is what keeps these substances the same size that they are. Anything that has gases in them, even you and I, we have to have air pressure in order to keep us the size that we are. So marshmallow is so nice and fluffy to eat because it has air bubbles inside and so when you're removing the pressure there's really no gas particles banging into the peep keeping it the size that it should be. at regular room pressure and so that's why you'll see the marshmallow expand.
And then eventually in the clip he shows that he lets the air pressure back in and the marshmallow will decrease in size because all those little bubbles have popped already. So atmospheric pressure as I already mentioned is the pressure caused by the air in our atmosphere. And it depends on the weather and altitude conditions.
As you see the altitude increase, your atmospheric pressure will decrease. And you would know this, especially if you went hiking, for example, in Colorado. It gets harder to breathe as you go up mountains because there is less oxygen available. If there's less oxygen, that means there's less particles colliding, and therefore there's less pressure. Standard pressure is the average pressure as measured at a specific level, and this is now C level.
Standard pressure equals three quantities. These three equalities all represent the same exact thing, they just have different units. So the first one is atmosphere. So one atmosphere is a standard pressure unit, 760 millimeters of mercury, and then finally 101.3. kilopascals or kPa.
When we talk about millimeters of mercury, we're literally talking about this thing called a barometer. So a barometer is a device used to measure atmospheric pressure. Basically the barometer is open to the atmosphere and the pressure pushing down on the mercury forces it up the tube and what you see for the height of the tube that, or excuse me, the height of the mercury in the tube is is going to tell you the pressure. So if you have any questions, make sure you direct your questions to your teacher, but I hope this video was helpful in understanding a little bit more about the kinetic molecular theory of gases.
Thank you so much for watching.