 So now let's take this idea of the ideal gas law ratio of problems and look at it a little bit more practically. So as a quick overview again, we had the ideal gas laws used in physics and we talked about how it could be divided for two different circumstances, same gas but two different times of measurements, and how for a closed system it reduces down to this basic equation. Now when it comes to using it, we don't always use this form. Sometimes there's even more simplifications that can happen. So I'm going to take a look at those simplifications and go through the algebra on some of those things. So let's say for example we have a situation with constant pressure and what that means is P1 is equal to P2 and in that case this equation can be reduced down to just V2 over V1 equals T2 over T1 because the pressures will divide out on the top and the bottom. Now depending on what things you're given, you can rearrange this equation to find any one of these individual quantities and to do that you're going to have to use the rules of algebra including those of cross multiplication to first work things out where you've got the denominators multiplied up and then dividing through to find the various quantities you want. So for example the V1 I'd have to divide through and I'd have T1 V2 over T2 and you can think of it as being the full this stuff on top and this one on bottom or you can think of it as being the T1 over T2 ratio multiplied by the other volume and similarly we could work out all of the other ones say solving for temperature 2 you'd end up with V2 over V1 times T1. You're always going to have two of the quantities on top of each other and then the other one off to the side. So just going through and showing this real quick again, you need to practice these sorts of algebra to understand why we get these relationships but then you can use them. I'm just going to offset this one a little bit so it's a little easier to read. So we have these relationships. Now real quick for this one, I'm going to talk a little bit about units. Your temperature must be in Kelvin. Absolutely must be no doubt nothing else can be possible. It must be in Kelvin. When it comes to the V2 and the V1, you need the same units for both volumes. The standard in physics would be used meters cubed but if you had leaders for both of them then when you put it into an equation like this last one you would end up having T2 equals, and I'm just going to make up some numbers here, three liters over two liters times the temperature, let's say that's 300 Kelvin. Well, when you do that calculation those liters on the top and the bottom cancel out and we end up with three halves of 300 and that would end up being 450 Kelvin. Check the math yourself. So we need to have the same units for both volumes but it could be meters cubed, it could be leaders. The temperatures must be the same and they must be Kelvin. So that's one example of a formula for constant pressure using those formulas. I'm going to do a couple other videos that talk about constant volume and constant temperature.