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Converting Between Moles and Liters of a Gas at STP

Feb 23, 2020
In this video we will learn how to convert

moles

and

liters

of a gas into STP. We'll do some problems like these and look at some common mistakes. Here is our first question: what is the volume and

liters

of 3.8

moles

of co2 gas in STP, let's talk about some information that will help us solve this problem first, what is STP, well, STP is an abbreviation for temperature and standard pressure, and the standard temperature and pressure are zero degrees Celsius and 1 atm, so whenever we are talking about something that happens in STP, it means that the temperature is zero degrees Celsius and the pressure is 1 atm.
converting between moles and liters of a gas at stp
Here is some other information that is really useful when we are in STP when we are at zero degrees Celsius from 1 atm. one mole of any gas takes up twenty 2.4 liters of volume, okay, twenty 2.4 liters, this is like a certain amount of space and that's how big 20 2.4 liters are. I made this box here, okay, so if we are in STP and we fill this we fill a box with gasoline or we had a balloon the size of this box and we fill it with gasoline, we would have one mole of gas here in these twenty 2.4 liters, okay, so using this information, let's think about this problem, okay? we have three point eight zero moles of co2 gas, okay, we know that STP, one mole of gas occupies twenty-two point four liters, okay, so if we had one mole of gas we would have twenty-two point four liters, that is the space that there would be.
converting between moles and liters of a gas at stp

More Interesting Facts About,

converting between moles and liters of a gas at stp...

We don't have a mole, we have three point eight zero moles, so we want to multiply this by twenty-two point four, which is the amount of space that one mole takes up in STP. Well, this is the method we use. To think about it now, let's look at how we could solve this using conversion factors. Well, we're starting with three point eight zero moles and now we want to multiply this by a conversion factor that will eliminate the moles and take two liters, okay, to do this we're going to want to take this information and write it as a conversion factor.
converting between moles and liters of a gas at stp
We could summarize this information as an equation like an equivalence like this or say that one mole is equal to or is equivalent to twenty-two point four liters, okay, now we have something very convenient, let's write down a conversion factor, okay, there are two conversion factors. possible conversions that we can write from an equation like this, okay, the first one we'll put up on this. the bottom is fine and it will look like a mole up about twenty 2.4 liters on the bottom. Now the other conversion factor that we can write from this is exactly the opposite, it just flipped, so we make 20 2.4 liters on the top and one. mole at the bottom, both are completely valid conversion factors.
converting between moles and liters of a gas at stp
We could use any of them, but in this problem we want to use a conversion factor that will remove moles from the top of this equation, so we're going to want to use a conversion factor that has moles at the bottom, so to For this particular problem we are going to use this conversion factor. Okay, now we have moles at the top and moles at the bottom, they will cancel and that will leave us. with liters and the calculations that we are going to do is multiply this divided by this and as you can see, dividing by one doesn't really change the value of something, so all the calculations that we did is multiply this, which is exactly the calculation that Se It happened to us when we were thinking about the problem.
Well, our final answer will be eighty-one eighty-five point one liters. We round this to three significant figures because there are three significant figures here, three significant figures here and this one. here's part of a definition, it's part of an equation like this, so we don't worry about this one, it has essentially an unlimited number of significant figures, so we round up to three eighty-five point one liters is how much space 3.8 0 moles of co2 gas would be consumed at STP ok let's move on ok I'm going to solve this problem and then talk about some common mistakes ok how many moles are there in 58.6 liters of nitrogen gas and two at STP?
Again here is the information we need in STP, one mole of any gas occupies twenty 2.4 liters of volume. So if we had 20 2.4 liters of nitrogen gas, we would have only one mole. We have more than 20 2.4 liters, so we are. we're going to have more than one mole and what we want to do is essentially know how many times twenty-two point four is fifty-eight point six, so we're going to do fifty-eight point six divided by twenty-two point four. Let's find out how many times this goes in and it will tell us how many moles fit into fifty-eight point six liters.
Okay, now to do this with conversion factors, we're going to start with 58.6 liters and we're going to take this relationship and think of it as an equation like this that will allow us to write down these two conversion factors and we'll choose the one that will eliminate the liters , which is at the top here. so it's going to be the one with liters at the bottom, move it over here liters cancel the leaders cancel it's going to leave us with moles and the calculations that we do are fifty-eight point six times one divided by twenty-two point four, which again, as you can see here, it's the same calculations that we do here, we're just thinking it through because this one doesn't really make a difference, all we're really doing is fifty-eight point six divided by twenty-two point four. the unit cancels out and we get two point six two moles rounding to three significant figures because this one here doesn't count since it's part of this official definition two point six two moles okay now, even if we're getting the hang of this Continue just for for a second because I want to talk about two super common mistakes that a lot of people make and I really don't want you to make them.
Well, here's the first super common mistake: what is the volume in liters of ten point three moles? of oxygen gas at 25 degrees Celsius and 2 ATM pressure, well, to solve this, many students would say that one mole of gas occupies twenty 2.4 liters of volume and I have ten point three moles instead of one mole, so I go to make ten point three times twenty-two point four and you can use conversion factors to do it like this, well, here's a trick, this is totally wrong, can you see why it has to do with this here in STP? One mole of gas is needed. up to twenty-two point four liters, but remember that STP is zero degrees Celsius and 1 atm, it is worth 25 degrees Celsius and two ATM is not STP in this whole thing where one mole equals twenty-two point four liters takes up twenty-two point four liters of space, just works in STP it only works at zero degrees Celsius and one ATM of pressure does not work in other conditions say twenty five degrees Celsius and two ATM of pressure so we cannot use this information to solve the problem unless we are in STP If you had To solve a problem like this, you would want to use the ideal gas law PV equals NRT because the ideal gas law works when you are not in STP.
I have a lot of videos on verifying the ideal gas law. Those, if you want to learn more, okay, here's another very common mistake. It's very complicated sometimes, teachers and textbooks, you really love this one. Okay, that's how it works. How many moles are there in 29.4 liters of liquid ethanol in STP? That's fine, and a student could figure it out. this problem like this is fine, why isn't it like this? Okay, we're in STP, so we can use one mole equals twenty, 2.4 liters and we can multiply it by this conversion factor, but can you see the trick here?
We're talking about quitting ethanol. Okay, and this idea of ​​one mole equals twenty. 2.4 liters only works with gases. Okay, so don't be fooled by this, always check that you are working with a gas in STP, not a liquid or a salt, so if the problem is to ask. about something that is liquid or solid you can't use one mole it takes up 22.4 liters you have to solve it in a different way basically don't be fooled by this don't trip up make sure you are talking about gas in STP, it is not something that is liquid or solid.
Now I'm going to ask two more questions where we just do some calculations between moles and liters, if you want to practice a little more, what volume with 0.73 five moles of O2 gas. They occupy one ATM of pressure and zero degrees Celsius. Well, first of all, we look at these conditions and we know that we are in STP, so we can use one mole equals twenty. 2.4 liters. Well, if we had one mole of O2 gas, it would take twenty 2.4 liters, we have less than one mole, so this amount of gas will take up less than twenty 2.4 liters, but still, to know how much space this would take up , we're going to want to take this amount of moles. and multiply it by the amount of space that one mole would take up in STP, that's how we think about it and now to use a conversion factor, we'll start with zero point seven three five moles and go to multiply it by a conversion factor made from this ratio, so here are our two options with this up, this down and flipped, we want to choose the one that will remove the moles, so we put it down and we put it right. here the moles cancel out the moles cancel out leaving us with liters multiplied by this divided by one it will be sixteen point five liters which as we predicted is a little less than twenty two point four liters we are going to make one plus 13 points zero liters of chlorine gas in STP they contain how many moles.
Well, we know we are in STP, so we can use this relationship. If we had twenty 2.4 liters of chlorine gas, we would have one mole. We have less than twenty 2.4 liters, so we'll have less than one mole, but basically we want to know how many times 22.4 fits in 213, so the math will be thirteen point zero divided by twenty-two point four or, with a conversion factor , it will be 13.0 liters multiplied by one of these conversion factors that we make from this relationship, we are going to choose one that puts liters at the bottom so that they cancel the liters at the top, the liters at the bottom cancel out, takes us with the moles and we're going to do this multiplied by one divided by this, the same calculations that we did here and our final answer will be zero point five eight zero moles, which is less than one mole because 13.0 liters is less than twenty-two point four liters, that's how you convert and vice versa between moles and liters of a gas in STP, the two things you always want to keep in mind is we want to make sure that the problem you're working with actually says it's at STP zero degrees Celsius and 1 atm if you are not zero degrees Celsius and 1 atm you cannot use this relationship between one mole and twenty 2.4 liters the second thing you should keep in mind is that we have to be talking about a gas even if it is something that is at zero degrees Celsius and 1 atm, if it is liquid or solid, you cannot use this relationship, so keep your eyes open and check this so you don't trip when doing these types of problems.

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