Name: Ideal gas law (PV=nRT)
Uploaded: 2020-04-23T18:46:14.000Z
Duration: 6 min 19 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

in this video, we're gonna talk about ideal gases and how we can describe what's going on with them.

Modal verbs - B1

So the first question you might be wondering is what is an ideal gas?

Adverbs of degree

And it really is a bit of a theoretical construct that helps us describe a lot of what's going on in the gas world, or at least close to what's going on in the gas world.

We imagine that the individual particles of the gas don't interact so particles articles don't interact, and obviously we know that's not generally true.

There's generally some light inter molecular forces as they get close to each other as they pass by each other, or if they collide into each other.

But for the sake of we're going to study in this video, we'll assume that they don't interact and will also assume that the particles don't take up any volume.

Now we know that that isn't exactly true.

That individual molecules, of course, do take up volume.

But this is a reasonable assumption because, generally speaking, it might be a very, very infinite presently small fraction of the total volume of the space that they're bouncing around it.

And so these are the two assumptions we make when we talk about ideal gases.

That's why we're using the word ideal in future.

Videos will talk about non ideal behaviour but allows us to make some simplifications that approximate a lot of the world.

So let's think about how we can describe ideal glad gases.

We can think about the volume of the container that they are in.

We could imagine the pressure that they would exert on, say, the inside of the container.

That's how I visualized it, although that pressure would be the same at any point.

Inside of the container, we can think about the temperature, and we want to do it in absolute scale.

So we generally measure temperature in Calvin.

And then we could also think about just how much of that gas we have, and we can measure that in terms of number of moles.

And so that's what this lower case and is.

So let's think about how these four things can relate to each other.

So let's just always put volume on the left hand side.

Well, what I imagine is if I have a balloon like this and I have some gas in the balloon if I try to decrease the volume by making it a smaller balloon without letting out any other air or without changing the temperature.

So I'm not changing t and n what's going to happen to the pressure?

Well, that gas is going to per square inch or per square area.

It gets harder and harder for me to squeeze that balloon so his volume goes down.

If I were to make the container bigger, not changing once again the temperature or the number of moles I have inside of the container, it's going to lower the pressure so it looks like volume and pressure move inversely with each other.

So we could say is that volume is proportional to one over pressure, the inverse of pressure.

Or you could say that pressure is proportional to the inverse of volume.

This just means proportional to which means that volume would be equal to some constant divided by pressure in this case.

Now, how does volume relate to temperature?

Well, if I start with my balloon example and you could run this example if if you don't believe me, if you take a balloon and you were to blow it up at room temperature and then if you were to put it into the fridge, you should see what happens.

Well, you could imagine that the particles inside the blue are a little less vigorous at that point.

They have lower individual kinetic energies, and so, in order for them to exert the same pressure to offset atmospheric pressure on the outside, you're going to have a lower volume.

And so volume, you could say, is proportional to temperature.

Now, how does volume compared to number of moles?

If you blow air into a balloon, you're putting more moles into that balloon and holding pressure and temperature constant, you are going to increase the volume, so volume is proportional to the number of moles of your take air out.

You're also going to decrease the volume keeping pressure and temperature constant so we can use these three relationships and these air actually known as this 1st 1 is known as Boyle's Law.

But you can combine them to realize that volume is going to be proportional to the number of moles times the temperature divided by the pressure, divided by the pressure or another way to say it is.

You could say that volume is going to be equal to some constant.

That's what proportionality is just talking about.

All of this business are and t Overbey over P or another way to think about it is we can multiply both sides by P and what will you get?

We will get p Times V, and this might be looking somewhat familiar to some of you is equal to, and I'll just change the order right over here.

And which is the number of moles Times some constant times T R.

Temperature measured in Calvin and this relationship right over here, P V is equal toe.

An RT is one of the most useful things in chemistry, and it's known as the ideal gas law on In future videos.

We're going apply over and over again to see how useful it is now.

One question you might be wondering is, What is this constant?

It's known as the ideal gas constant, and you can look it up.

 But it's going to be dependent on what units you use for a pressure, volume and temperature, and we will see that in future videos. 