Be Lazy! Don't Memorize the Gas Laws!

Well, here are many of the gas equations we've talked about. Who wants to

memorize

them all? I have to because I'm going to show you an incredibly useful trick in this video so you never have to worry about memorizing all of these types. Is that how it works. All you have to remember is that the ideal gas law PV equals NRT and it is kind. sounds great, so it's very easy to remember that PV is equal to NRT and you can use that to get any of these other gas

laws

whenever you need them to solve a problem, so we can put all these guys in because we don't need a none of them and I'm going to show you how to use PV equals NRT for this trick, so let's say you are presented with a problem like this, okay, we have a before and after, we have pressure and temperature or both change, so we look at the variables we are dealing with.

I just said pressure and temperature and what I want to do is take PV equals NRT, the ideal gas law and rearrange it so that the variables I'm interested in pressure and temperature are on their own on one side of the equation, it doesn't matter which side is okay, then pressure and temperature, to get P and T by themselves, I will first divide both sides by V years and then V over V. I will cancel them, so now I have P equal to NRT divided by V and I want to get T on the other side of the equation so that it can join P so I will divide both sides by T and now T over T cancels out and I'm left with PT P over T equals NR over feet, okay, so we have P over T on one side of the equation, now it turns out that if something is on one side of the ideal gas equation, you can duplicate it on the other side by doing it before and after this is what I mean , we can take this P over T and convert it to p1 over t1 there is a before and then we double it on the other side is equal to p2 over t2 what we actually just did is we created gay lussac's law, but I didn't have to

memorize

it and all I had to do is take PV equals NRT and then figure it out from there, okay, let's look at another example, here's one where I have an initial pressure and an initial final pressure. volume and final volume, so the variables I'm interested in are pressure and volume as before.

I want to rearrange the equations to have the pressure and volume alone on one side. Hell, it's easy, the ideal gas

laws

are already written, so pressure and volume. or by themselves on one side, so what we do now is we double this PV on both sides of the equation by doing before and after, so that p1 times v1 is equal to double on the other side p2 times v2 and now I can plug my variables and solve for v1 and check it. What I did was I used PV equals NRT to arrive at Boyle's law.

Okay, you're probably getting the hang of it by now. I'm going to do two more examples, two more examples, but if this already makes sense, go ahead and move on. A question I often get is how do you know which variables you want to rearrange the equation? You know, teachers and textbooks don't always ask questions where they just say v1 is this and one. it's this and so on, so if you're given a word problem, it can be a little bit trickier to figure out what variables you're using, are they v1n 2 or whatever, if you're having trouble figuring out what the problem is.

The variables are watch my video called What Gas Equation Do I Use and it will tell you how to read a word problem and determine which of the variables you are working with. Okay, so in this one we'll use volume. and moles, then we want to rearrange the ideal gas law so that it has volume and moles on its own on one side, okay, I'll get rid of P so that it only has V on this side, divide both sides by P and then I have V . is equal to n R T divided by P and I want to take n to the other side, so I'm going to divide both sides by n here cross it out and then I have V over N equals RT over P.

I have this guy alone, so let me double it. before and after both sides the equal sign V 1 over N 1 is equal to V 2 over n 2 and what I did there was I came up with Avogadro's law one plus this is for 1 it's a little more complicated I have a before and an after here, where three variables are changing, I have volume pressure and temperature, so everything I've been doing up to this point has only had changes in two variables, but it's no big deal, you can use this technique for any number of variables, so volume pressure - temperature I want to be on one side of the ideal gas equation, so I already have pressure in volume here, so how about I divide both sides by T to put them all together?

Cancel this and you know I'm rewriting it, but it doesn't really matter what's on the right side here, all that matters is what's on the left side here when we put them together, so now I change this to p1 for v1 over t1 , double on the other side is equal to p2 times v2 over t2. and there was where is here that was the combined gas law, but hey, I didn't have to memorize it, that's how you can use this technique to find any of the gas equations that you need and not have to worry about them. memorizing, but you'll need to be able to read a written problem and figure out which of the variables you're working with, so again, if you're having trouble with that, watch the video I talked about earlier and you should be ready.