 So this is the setup for an example problem, which works with the ideal gas law using the physics units. And again, in physics, the version of the ideal gas law we use is this pv equals nrt. And in physics, we typically use the r value of 8.314 joules per mole kelvin. And in my other video where I introduced the ideal gas law, I explained why these are the logical units to use for physics. In contrast, when you get a problem, you might not have things in the correct physics units. You might be given things in liters and in Celsius and in atmospheres. So in this example problem for my students, we're actually going to go through and talk about what you have to do to convert these into the standard physics units to be able to solve the problem. Now, in this case, we're first working with the pressure. And I always encourage my students to take a moment before they start trying to calculate things and identify the values they're given. So a pressure is going to be this value for atmospheres. So they gave us a value of pressure as 7.00 atmospheres. But we don't want atmospheres in the physics. We want to actually use the standard physics units of Pascal's. So we're going to have to set up a unit conversion here. And again, because I've got atmospheres on the top, I want to want to have atmospheres on the bottom and Pascal's up on top. And if you go look this up, you'll see that one atmosphere is equivalent to 1.013 times 10 to the fifth Pascal's. So if you complete this, you would cancel out the atmospheres, multiply your 7 by the 1.013 times 10 to the fifth. And you will actually get your pressure in Pascal's. So I'm not going to do this step because I want my students to do this step. Then we move on to the next part here, the volume. And again, going back to what we've been given, liters is a unit for volume. So we've actually been given the volume as 5.00 liters. But in physics, we want to use meters cubed. So again, we've got to set up a conversion factor here where we're going to have liters on the bottom and meters cubed up on the top. And the conversion factor is 1 liter is equal to 1 times 10 to the minus 3 meters cubed. So you can go through and do this calculation. The liters would cancel out and you're going to come up with a value in meters cubed. Again, my students need to do this calculation on their own. Then we get to temperature. Now, whether you're in physics or chemistry or anything else, our temperature has to be in units of Kelvin. So this isn't a physics versus chemistry type thing. If I've given the temperature in Celsius degrees in order to use the ideal gas law, I have to have it in the temperature units of Kelvin. So this is not just a normal unit conversion. We have to actually use the equation, which tells us that the temperature in Kelvin is equal to the temperature in Celsius plus 273. Now technically it's 273.15 in order to do that conversion. Since we've got everything to three significant digits, you can just use the 2.73. It won't make a big difference on your calculation. And when you do that, you'll have a temperature in Kelvin rather than in Celsius. Once we've done those things, then my students can move to the very last step. Which is actually solving this problem for the number of moles of the gas in the vessel. So all these steps we've done previously are just setting things up into the current units. Because I've got my equation PV equals nRT. P is pressure, V is volume, T is the temperature, R is the universal gas constant. We're actually asking here what is n, the number of moles. So we're going to have to do a little algebra first. And if you're struggling with algebra rearrangements, check with me or one of your other classmates to make sure you understand how we get this equation. But the number of moles is going to be equal to PV divided by the RT. You would then plug in that value you got in Pascal's. And that volume you got in meters cubed. And divide it by our 8.314 joules per mole K. And the value you got for the temperature in Kelvin. Now notice here I'm putting in these extra parentheses on the bottom. Because for most of you when you put things in your calculator, if you just use parentheses times something in parentheses divided by parentheses times something in parentheses, it's going to take this second quantity and actually multiply it rather than put it on the bottom. So depending on the type of calculator you have, appropriate use of those extra parentheses on the bottom is crucial for you to actually get the correct answer, which should be a number in moles. Again, if you need to go back and watch the introduction to PV equals RT, to make sure you understand what all of these quantities are and what sort of units you should be working with.