Understanding Properties of Gases

Properties of gas is going to be the topic of this lesson, and I want to talk a little bit about what distinguishes a gas from a liquid or a solid, and then we're going to spend a little time talking about one of those things, which is pressure. That'll pretty much be it for this lesson. My name is Chad, and welcome to Chad's Prep, where my goal is to take the stress out of learning science. In addition to high school and college science prep, we also do MCAT, DAT, and OAT prep as well. You can find those courses at chadprep.com. Now this lesson's part of my new general chemistry playlist. I'm releasing several lessons a week throughout the entire school year. So if you want to be notified every time I post one, subscribe to the channel, click the bell notification. All right, so let's talk about gases. I am reminded of an evening where I had a splitting headache and I could not sleep that night because of this splitting headache. And so I got up to get a couple of ibuprofen and I didn't want to turn on any lights so as to wake anybody up and stuff like this. So I knew the size of the bottle. I knew the size of the pills in the bottle. And so... I felt around and found the right bottle and had the right size pills in it. I took a couple and my headache never went away. And in the morning, I discovered my mistake and my error was that I had taken, instead of two ibuprofen, two stool softeners instead. Oh, wait a minute. That's the wrong discussion about gases. Another story. My bad. Completely irrelevant, but completely true as well. But not the discussion of gases we're about to have. So we need to talk about gases and first distinguish them between both liquids and solids. And you should know that a gas does not... have a definite shape or volume. It will take on the shape and volume of whatever container you stick them in. And that's different than a liquid. A liquid will take on the shape of the container, but it's not going to expand so as to fill up the container. So we'd say a liquid has a definite volume, but not a definite shape. And then a solid is going to have both definite shape and definite volume. And so that's how you should know basically how we distinguish a gas from either liquid or solid. So again, gases, no definite shape and no definite volume. Liquids, definite volume, but no definite shape. And then solids, definite volume and definite shape. Cool. So it turns out one of the reasons for this is that gases are made up of mostly empty space under a lot of conditions. Whereas a liquid or a solid is going to actually be, you know, molecules or atoms pretty close in contact. And as a result, you know, these gases, it turns out, because they're mostly made of empty space, they can spread out to fill a container. But it also makes them very compressible. And so you can bring the molecules and atoms closer together by putting a bunch of... pressure on the gas and filling up some of that empty space with more molecules and atoms and things of the sort. So we say that gases are rather compressible, but in comparison, liquids and solids, not very compressible at all. So you can definitely jack up the pressure on a liquid or a solid, but you are going to get a very, very, very tiny volume change as a result. Whereas gas, the more you jack up the pressure, the smaller that volume is going to get. And we'll find out that pressure and volume will actually be inversely proportional under a lot of conditions. We also want to talk about one last thing, and that is that gases will mix with other gases in pretty much any proportion. Notice this is not true for liquids, say. Like, you know, if you try to mix oil and water, they're going to form two layers. And that's because the oil molecules and the water molecules don't like each other. Not a very technical way to put it. It really comes down to intermolecular forces and entropy, which we'll talk about in the next chapter. But they don't like each other. So with gases, though, because... the molecules or atoms are separated by mostly empty, you know, fair amount of empty space, it doesn't matter if they like each other or not, they're going to be separated by empty space. And so they pretty much can mix in any proportion. If you, you know, look at the air in this room around me, you know, like 78% of it is nitrogen and 21% is oxygen. There's trace amounts of other stuff. And it turns out, you know, you could raise the amount of oxygen or lower the amount of oxygen and it would mix with the nitrogen no matter, you know, the proportion. So gases will mix with other gases in any proportion. That's not always going to be true. For liquids and solids, obviously, are difficult to mix in the same kind of sense. Cool. And going back to the compressibility of gases, as a result of their compressibility, we often talk about pressure with respect to gases in a way that we probably wouldn't talk about it with liquids or solids. Now, we can talk about pressure on solids and things of this sort, and you might do that in a physics context or an engineering context a little bit. But again, they're largely incompressible. And so you'd be talking about crazy amounts of pressure to cause very tiny amounts of a volume change in things of the sort. So with the gas, that's not that way. And so pressure is very relevant to talking about a gas. And so first I'm going to talk about though is what in the world is pressure? So we have a mathematical definition and it is force per unit area. So it turns out that that force in SI units would be Newtons and the SI unit for area is meters squared. And it turns out this is the same thing as a Pascal. And so the Pascal, which is a Newton per meter squared is the SI unit for. pressure. So but it's also one we're just not going to all that commonly use in a chemistry context. In a physics class you'd probably use it quite often but you're going to find out that we're probably going to use atmospheres more commonly than anything else and maybe tor or millimeters of mercury as we'll see a little bit as well. So I'm not saying you can't use Pascal, and we'll go through the conversion here in a little bit, but you're probably going to use it less commonly. And so this is an area where we won't use the SI unit as much as, say, a non-SI unit like the atmosphere. Okay, so if you take a look at this definition, a couple things you should understand. So let's just say, for instance, that maybe you did not like my opening discussion about stool softeners, and you thought it was vulgar and disgusting, and you're angry at me, and so you decide that you're going to stab me in my watermelon. one of the ones out back in the garden. And so you decide you're going to stab it with this lovely marker, with the butt end of this marker. And you're going to stab it and you're going to hit it. So, and the question is, should you stab it with this marker or should you stab it with a knife? Which one has a better chance of piercing the skin of that watermelon, the marker, the butt end of a marker, or the nice tip end of the knife? Obviously this is being a little facetious here and I don't know, you're just weird wanting to stab my watermelon anyways. I don't know what's wrong with you. But the idea is that you have a much better chance of piercing the skin of that watermelon with the knife. And the idea is, let's say you hit the watermelon as hard as you can in either case, you're applying the same force in either case, but the tip of the knife has a much smaller surface area over which you're applying that force. And so pressure, while it's directly proportional to force, it's inversely proportional to that area. And so a much smaller area is going to lead to a much higher pressure that is generated at the tip of that knife. And so and that higher pressure is going to have a much greater chance of actually piercing the skin of that watermelon. And again, I still don't know why you're doing that. It's just weird. Leave my garden alone. All right, so you should understand that relationship. Pressure is directly proportional to force, but inversely proportional to area. And then you should just be familiar with some of the units and how we convert back and forth with them. And so the most common unit we will use is the atmosphere. And it turns out this is just the air pressure at sea level on planet Earth. one atmosphere and hence the name. And it turns out if you look at what's causing this, it's just the weight of all the air above you when you're there at sea level. And that's why if you like climb up a tall mountain and stuff like that, you're going to have less air in the atmosphere above you. And so you're not going to be as great a pressure. And so as you go up in elevation, your pressure goes down lower and lower and lower below one atmosphere. Cool. So that's where the atmosphere comes from. You might express this in some other units. And one of those units is the millimeter of mercury. And this is kind of a weird unit, but it comes from the old manometers and barometers that used mercury, a column of mercury. And it turns out that one atmosphere could push down into a fluid to cause that column of mercury to rise to a height of 760 millimeters when it was a one atmosphere pressure, you know, causing that change in height. And so that's where that kind of comes from. But now we just so commonly use it, and it's one you should know. And it turns out... We can also relate this to 760 Tor. So it turns out this whole height of the millimeters of Mercury, well, that depends on if you're on planet Earth at sea level. So, and maybe you're not on planet Earth. Maybe you're on Jupiter, which, you know, would be a totally, want a different atmosphere, but also the column would rise to a different height. And so they wanted to come up with a unit that was kind of independent of what, you know, what gravitational field you're experiencing. So they came up with Tor. And as long as you're at the surface of the Earth at sea level, Then millimeters of mercury and tor are the same thing, and that's pretty much what you're just going to assume at all times in this class. Cool, and then we got the pascal, and it turns out there's 101,325 pascal equal to one atmosphere. This is about 100,000, about 10 to the fifth pascal is a nice rule of thumb. So every 100,000 pascal is an atmosphere, and sometimes we'll put this in kilopascal, and it'd be 101.325 kilopascal. So, and again, you're much more commonly going to see atmospheres, millimeters, mercury, and torr than you probably are pascal or kilopascal, but I can't rule it out, especially for some of your classes. And again, some of you guys might not see it at all. So, but some of you might actually have some, at least small number of conversions involving pascal. If you are in the good old US of A, you'll find out that, you know, if you're airing up your bike tire or your basketball or your car tire or things of a sort, you're probably going to see pressure measured much more commonly in. PSI, which is pounds per square inch. And the pounds is the measure of the force and the per square inch, the measure of the area there. But again, probably not something you're actually going to encounter here in chemistry land. So great. And if you want to compare it to the things you're learning, it's between 14 and 15 PSI equal to an atmosphere. I think like 14.7 PSI equals one atmosphere, but again, not largely something you're going to use inside your general chemistry course. Okay, so let's just take a look at a typical, you know, conversion you might see here. And let's just say that we've got two atmospheres and we want to convert this into, say, tor. Okay, well, in this case, we put our ATMs on the bottom, we put our tor on top. And basically, our equivalence here is based what we use our conversion factor. So one atmosphere is equal to 760 tor. So we just multiply across and 2 times 760 here, so is going to equal, so 2 times 700, if you want to do this in your head, is 1400. And then the 60 is going to get us to 1520 tor there. So what if we wanted to go to Pascal? So in this case, 2 atmospheres. So in this case, 1, if it's a nice round number, you could be like, well, again, 1 atmosphere is about 100,000, so 2 atmosphere about 200,000. And at least you'd know how to approximate it off the top of your head there. So we put atmospheres down here, pascals up top, and again, one atmosphere is going to equal 101,325 pascal, and that's a really ugly 5. If you've ever noticed, I make my 5s upside down. I start at the bottom and work my way up because I'm just weird like that. And now you'll notice every time I make a 5. Notice how many 5s are on this board? Only 1, 2, 3, 4, so it'll bug you now every time you see it in one of my videos. Alright, so 2 times 101,325 is going to be 202,650 Pascal. Cool, and that's another number 5. If you missed that one, you might rewind it and take a look real quick. Cool, but that's it. That's the kind of conversions we might be doing somewhere along the way, and you'll find out that rather than converting from atmospheres into tor or Pascal, it's probably actually going to be more likely the other way. We'll find out a lot of the calculations we do. are going to require you to put the pressure in atmospheres. And so maybe you'll see it going the other direction. But similar to some of the conversions we've done, and in some of the other lessons, we'll actually carry out some more of these conversions along the way of solving some of the other calculations we do. Now, if you found this lesson disgusting or vulgar or annoying, then hit that like button. That's exactly how you should let me know. The more likes I get, the more I know. And we'll refrain in the future. If you are looking for practice materials on gases or anything else in general chemistry, check out my General Chemistry Master Course. Over 1,200 questions, quizzes, chapter tests, practice final exams, final exam rapid reviews. I'll leave a link in the description. Free trials available. Happy studying.

You can find those courses at chadprep.com. Now this lesson's part of my new general chemistry playlist. I'm releasing several lessons a week throughout the entire school year. So if you want to be notified every time I post one, subscribe to the channel, click the bell notification. All right, so let's talk about gases.

I am reminded of an evening where I had a splitting headache and I could not sleep that night because of this splitting headache. And so I got up to get a couple of ibuprofen and I didn't want to turn on any lights so as to wake anybody up and stuff like this. So I knew the size of the bottle.

I knew the size of the pills in the bottle. And so... I felt around and found the right bottle and had the right size pills in it.

I took a couple and my headache never went away. And in the morning, I discovered my mistake and my error was that I had taken, instead of two ibuprofen, two stool softeners instead. Oh, wait a minute. That's the wrong discussion about gases.

Another story. My bad. Completely irrelevant, but completely true as well. But not the discussion of gases we're about to have. So we need to talk about gases and first distinguish them between both liquids and solids.

And you should know that a gas does not... have a definite shape or volume. It will take on the shape and volume of whatever container you stick them in. And that's different than a liquid. A liquid will take on the shape of the container, but it's not going to expand so as to fill up the container.

So we'd say a liquid has a definite volume, but not a definite shape. And then a solid is going to have both definite shape and definite volume. And so that's how you should know basically how we distinguish a gas from either liquid or solid.

So again, gases, no definite shape and no definite volume. Liquids, definite volume, but no definite shape. And then solids, definite volume and definite shape. Cool. So it turns out one of the reasons for this is that gases are made up of mostly empty space under a lot of conditions.

Whereas a liquid or a solid is going to actually be, you know, molecules or atoms pretty close in contact. And as a result, you know, these gases, it turns out, because they're mostly made of empty space, they can spread out to fill a container. But it also makes them very compressible. And so you can bring the molecules and atoms closer together by putting a bunch of...

pressure on the gas and filling up some of that empty space with more molecules and atoms and things of the sort. So we say that gases are rather compressible, but in comparison, liquids and solids, not very compressible at all. So you can definitely jack up the pressure on a liquid or a solid, but you are going to get a very, very, very tiny volume change as a result. Whereas gas, the more you jack up the pressure, the smaller that volume is going to get. And we'll find out that pressure and volume will actually be inversely proportional under a lot of conditions.

We also want to talk about one last thing, and that is that gases will mix with other gases in pretty much any proportion. Notice this is not true for liquids, say. Like, you know, if you try to mix oil and water, they're going to form two layers. And that's because the oil molecules and the water molecules don't like each other.

Not a very technical way to put it. It really comes down to intermolecular forces and entropy, which we'll talk about in the next chapter. But they don't like each other.

So with gases, though, because... the molecules or atoms are separated by mostly empty, you know, fair amount of empty space, it doesn't matter if they like each other or not, they're going to be separated by empty space. And so they pretty much can mix in any proportion. If you, you know, look at the air in this room around me, you know, like 78% of it is nitrogen and 21% is oxygen. There's trace amounts of other stuff.

And it turns out, you know, you could raise the amount of oxygen or lower the amount of oxygen and it would mix with the nitrogen no matter, you know, the proportion. So gases will mix with other gases in any proportion. That's not always going to be true.

For liquids and solids, obviously, are difficult to mix in the same kind of sense. Cool. And going back to the compressibility of gases, as a result of their compressibility, we often talk about pressure with respect to gases in a way that we probably wouldn't talk about it with liquids or solids. Now, we can talk about pressure on solids and things of this sort, and you might do that in a physics context or an engineering context a little bit. But again, they're largely incompressible.

And so you'd be talking about crazy amounts of pressure to cause very tiny amounts of a volume change in things of the sort. So with the gas, that's not that way. And so pressure is very relevant to talking about a gas.

And so first I'm going to talk about though is what in the world is pressure? So we have a mathematical definition and it is force per unit area. So it turns out that that force in SI units would be Newtons and the SI unit for area is meters squared. And it turns out this is the same thing as a Pascal.

And so the Pascal, which is a Newton per meter squared is the SI unit for. pressure. So but it's also one we're just not going to all that commonly use in a chemistry context.

In a physics class you'd probably use it quite often but you're going to find out that we're probably going to use atmospheres more commonly than anything else and maybe tor or millimeters of mercury as we'll see a little bit as well. So I'm not saying you can't use Pascal, and we'll go through the conversion here in a little bit, but you're probably going to use it less commonly. And so this is an area where we won't use the SI unit as much as, say, a non-SI unit like the atmosphere.

Okay, so if you take a look at this definition, a couple things you should understand. So let's just say, for instance, that maybe you did not like my opening discussion about stool softeners, and you thought it was vulgar and disgusting, and you're angry at me, and so you decide that you're going to stab me in my watermelon. one of the ones out back in the garden.

And so you decide you're going to stab it with this lovely marker, with the butt end of this marker. And you're going to stab it and you're going to hit it. So, and the question is, should you stab it with this marker or should you stab it with a knife?

Which one has a better chance of piercing the skin of that watermelon, the marker, the butt end of a marker, or the nice tip end of the knife? Obviously this is being a little facetious here and I don't know, you're just weird wanting to stab my watermelon anyways. I don't know what's wrong with you. But the idea is that you have a much better chance of piercing the skin of that watermelon with the knife.

And the idea is, let's say you hit the watermelon as hard as you can in either case, you're applying the same force in either case, but the tip of the knife has a much smaller surface area over which you're applying that force. And so pressure, while it's directly proportional to force, it's inversely proportional to that area. And so a much smaller area is going to lead to a much higher pressure that is generated at the tip of that knife. And so and that higher pressure is going to have a much greater chance of actually piercing the skin of that watermelon. And again, I still don't know why you're doing that.

It's just weird. Leave my garden alone. All right, so you should understand that relationship.

Pressure is directly proportional to force, but inversely proportional to area. And then you should just be familiar with some of the units and how we convert back and forth with them. And so the most common unit we will use is the atmosphere. And it turns out this is just the air pressure at sea level on planet Earth. one atmosphere and hence the name.

And it turns out if you look at what's causing this, it's just the weight of all the air above you when you're there at sea level. And that's why if you like climb up a tall mountain and stuff like that, you're going to have less air in the atmosphere above you. And so you're not going to be as great a pressure. And so as you go up in elevation, your pressure goes down lower and lower and lower below one atmosphere. Cool.

So that's where the atmosphere comes from. You might express this in some other units. And one of those units is the millimeter of mercury.

And this is kind of a weird unit, but it comes from the old manometers and barometers that used mercury, a column of mercury. And it turns out that one atmosphere could push down into a fluid to cause that column of mercury to rise to a height of 760 millimeters when it was a one atmosphere pressure, you know, causing that change in height. And so that's where that kind of comes from.

But now we just so commonly use it, and it's one you should know. And it turns out... We can also relate this to 760 Tor. So it turns out this whole height of the millimeters of Mercury, well, that depends on if you're on planet Earth at sea level. So, and maybe you're not on planet Earth.

Maybe you're on Jupiter, which, you know, would be a totally, want a different atmosphere, but also the column would rise to a different height. And so they wanted to come up with a unit that was kind of independent of what, you know, what gravitational field you're experiencing. So they came up with Tor. And as long as you're at the surface of the Earth at sea level, Then millimeters of mercury and tor are the same thing, and that's pretty much what you're just going to assume at all times in this class.

Cool, and then we got the pascal, and it turns out there's 101,325 pascal equal to one atmosphere. This is about 100,000, about 10 to the fifth pascal is a nice rule of thumb. So every 100,000 pascal is an atmosphere, and sometimes we'll put this in kilopascal, and it'd be 101.325 kilopascal. So, and again, you're much more commonly going to see atmospheres, millimeters, mercury, and torr than you probably are pascal or kilopascal, but I can't rule it out, especially for some of your classes.

And again, some of you guys might not see it at all. So, but some of you might actually have some, at least small number of conversions involving pascal. If you are in the good old US of A, you'll find out that, you know, if you're airing up your bike tire or your basketball or your car tire or things of a sort, you're probably going to see pressure measured much more commonly in. PSI, which is pounds per square inch.

And the pounds is the measure of the force and the per square inch, the measure of the area there. But again, probably not something you're actually going to encounter here in chemistry land. So great. And if you want to compare it to the things you're learning, it's between 14 and 15 PSI equal to an atmosphere.

I think like 14.7 PSI equals one atmosphere, but again, not largely something you're going to use inside your general chemistry course. Okay, so let's just take a look at a typical, you know, conversion you might see here. And let's just say that we've got two atmospheres and we want to convert this into, say, tor.

Okay, well, in this case, we put our ATMs on the bottom, we put our tor on top. And basically, our equivalence here is based what we use our conversion factor. So one atmosphere is equal to 760 tor.

So we just multiply across and 2 times 760 here, so is going to equal, so 2 times 700, if you want to do this in your head, is 1400. And then the 60 is going to get us to 1520 tor there. So what if we wanted to go to Pascal? So in this case, 2 atmospheres.

So in this case, 1, if it's a nice round number, you could be like, well, again, 1 atmosphere is about 100,000, so 2 atmosphere about 200,000. And at least you'd know how to approximate it off the top of your head there. So we put atmospheres down here, pascals up top, and again, one atmosphere is going to equal 101,325 pascal, and that's a really ugly 5. If you've ever noticed, I make my 5s upside down.

I start at the bottom and work my way up because I'm just weird like that. And now you'll notice every time I make a 5. Notice how many 5s are on this board? Only 1, 2, 3, 4, so it'll bug you now every time you see it in one of my videos. Alright, so 2 times 101,325 is going to be 202,650 Pascal. Cool, and that's another number 5. If you missed that one, you might rewind it and take a look real quick.

Cool, but that's it. That's the kind of conversions we might be doing somewhere along the way, and you'll find out that rather than converting from atmospheres into tor or Pascal, it's probably actually going to be more likely the other way. We'll find out a lot of the calculations we do.

are going to require you to put the pressure in atmospheres. And so maybe you'll see it going the other direction. But similar to some of the conversions we've done, and in some of the other lessons, we'll actually carry out some more of these conversions along the way of solving some of the other calculations we do. Now, if you found this lesson disgusting or vulgar or annoying, then hit that like button.

That's exactly how you should let me know. The more likes I get, the more I know. And we'll refrain in the future. If you are looking for practice materials on gases or anything else in general chemistry, check out my General Chemistry Master Course.

Over 1,200 questions, quizzes, chapter tests, practice final exams, final exam rapid reviews. I'll leave a link in the description. Free trials available. Happy studying.

Transcript for:Understanding Properties of Gases

Transcript for:
Understanding Properties of Gases