Which gas equation do I use?

So how do you choose the correct gas law when trying to solve a problem that will be the focus of this video? Maybe you're already ready when someone tells you that okay, use Boyle's law for this question and Charles's law for this question, but then you get a little taken aback when they give you a question and you have to figure out

which

of these laws of the gases you use to solve it. We will see it here, this video may also be useful to you if you are having trouble deciphering the variables in an

equation

, in other words, if you are having difficulty reading a question, determining what should be v1 and what should be p2, watch how They bring both things together and we will use it to help.

Let's solve these

equation

s, so the first question here is that a sample of gas occupies 45 liters after being compressed to a volume of 12 liters. The sample has a pressure of 5.7 atm, what was the original pressure? So when you solve these gas problems, the first thing to think about when reading a question is if there is a change happening, if there is a before and after, then is there a before and after with this question? Yes, a sample of gas occupies 45 liters and is then compressed to a volume. 12 liter, so I'm going to write these variables down so we can keep track of them and that can be a useful thing to do at first before you get the hang of it.

Well, there is a before and after. before we have a volume v1, the initial volume of 45 liters, then we have this after the volume, the volume is compressed up to 12 liters, so that is before and after the volume, what about other variables, then we have this pressure of 5.7 atm, what is this after being? Compressed, the sample has a pressure of 5.7 atm,

which

means that the pressure p2 here is 5.7 atm because it was after this change occurred and the question is what was the original pressure, so what was the pressure before this change? This p1 is where we are.

Let's solve, so we set up and calculate the variables like this. Now we need to determine which of these gas laws we are going to use. We want to find the gas law that has V 1 and P 1 and V. 2 and P 2 1 and that will be Boyle's law because the variables we are solving coincide with the variables in the equation, let's look at another one: a balloon occupies 32 liters of volume at 20 degrees Celsius and a pressure of 212 kiloPascals. At what temperature will the balloon have a volume of 50 liters and a pressure of 300 kiloPascals? So, just like before, we want to ask about a change.

There is a change? Is there a before and after here or maybe there are just two different ones? Well, there are situations because we start with this volume, temperature and pressure and then you ask what temperature these other things will be okay at, then that would be a change to another set of circumstances, so the original temperature will be the temperature. um 20 degrees Celsius and temperature - at what temperature did this happen? That's what we're solving. Well, let's look at the other variables. Let's start with the volume. Okay, volume. The balloon initially occupies 32 liters, so that's v1.

There is a volume change in what. The temperature would be that volume, where would that balloon have a volume of 50 liters? So that's what it would be after this change, we have 50 liters and how's the pressure? Our initial pressure before changing the temperature is 212 kPa and then we change the temperature t2 and We are looking for a pressure of 300 kilo Pascal, so there are variables here. Which of these equations has the variables we are looking for? We want t 1 V 1 P 1 and T 2 V 2 and P 2, so we're going to I'll be using the combined gas law because all of these guys fit together and we're going to rearrange them to solve for t2.

Well, those two examples we looked at were relatively simple. Now I'm going to do some that are a little more complicated because they have some of them have additional information in their content, sometimes they confuse people, so here we go as I read it. I want you to think if there is a change, there is a before and after and then we will see how we configure. The variables are fine at a temperature of 65 degrees Celsius and a pressure of 1120 millimeters of mercury. A large balloon occupies 25 liters. What will be the volume if the pressure is reduced to 5 degrees Celsius? well, is there absolutely a change due to the 65 degree temperature? which is then lowered to 5 degrees Celsius, so we have a temperature before and after, so before and after the temperature before is 65 degrees Celsius, the temperature after we lower it to 5 degrees Celsius 5 degrees Celsius, let's see what is happening with the other. variables now, we have a pressure of 1120 millimeters of mercury, so we can call that p1 millimeters of mercury, what happens to the pressure?

The pressure doesn't change, there's no p2, we'll come back to that in a minute, let's look at the volume here. at the initial temperature we have a volume of 25 liters, well v1 is 20 liters, 25 liters and it says what the volume will become if the temperature is lowered, so it is this later volume that we are going to solve for, so the variables In the problem t1 t2 v1 v2 and p1 are given a pressure, but here is one thing that p1 does not change, it was given to us at the beginning, but there is no p2, there is no after, so we assume that p1 remains the same. what we call a constant is something that does not change during the course of the equation because p1 does not change, we do not want p1 to be in the equation that we use, so don't get confused and use the gas law combination because it has these types in its First, we don't worry about p1 because it doesn't change and we just want an equation that has T 1 V 1 T 2 and V 2, so we'll use Charles's Law, solve for just these things that change and have a before and after and leave out to these guys like p1 which are our constants that don't change over the course of the problem, so if one of these questions gives you something extra Don't get sidetracked, just ask yourself whether or not it changes over the course of the problem, if not , leave it out.

Okay, at a temperature of 45 degrees Celsius and a pressure of 250 kilograms Pascal, how many moles will be filled into a container? 16 liters of volume ok as before there is a change here there is a before and after no there is no no change here the variables we have a temperature of 45 degrees Celsius you have a pressure of 250 kilo Pascal the question is how many moles fit in a container that fits this description, so let's solve for moles and this is a container that has a volume of 16 liters. These are the variables, but there is no before and after, so you have to figure it out. for the moles here we want to use the only equation here that does not have a before and an after, it does not have a 1 and a 2 and that is up to here the ideal gas law, it has P V N and T and we know what R is, it is a gas constant, but there is no change in this equation, so the ideal gas law is the equation you want to use whenever you solve a gas problem like this, it gives you these variables, but it doesn't not have a before and one after the two different configurations, that's fine, one more, this one is long and you can guess it has additional information, we will find out what we need and what we don't think about again for a change.

Is a change happening and what is it? A gas sample in a twenty liter rigid container has a pressure of 2,200 millimeters of mercury and is placed outside in the morning when the temperature is cold during the day and warms in the afternoon. the pressure reaches 39 degrees Celsius, okay, right there when we change from cold to hot, then there is a change in pressure, I mean, sorry, a change in temperature, okay, anyway it reaches 39 degrees Celsius and the pressure inside the container is 2700 millimeters of mercury. What was the temperature in the morning, so we have a before and after, the temperature after we know immediately t2 is 39 degrees because we said it was cold in the morning, it was hot the question is what was the temperature in the morning So what was the temperature? before the warm up, it will be t1 and we don't know what it is, that's what we're going to figure out.

Let's look at these other numbers. Here we say there is a sample of gas in a 20 liter rigid container so we can say something like v1 is 20 liters, does v1 change throughout this equation throughout this question? Could you read this no, there is no other mention of the volume changing, so we will assume that the volume is constant at all times and it is not something we need to worry about when choosing an equation. Well, let's look at the other numbers. Here we have a pressure, this is in the morning, of 2,200 millimeters of mercury, so I will call that pressure one two thousand two hundred. millimeters of mercury, is that change worth it?

Is there a subsequent pressure? Yes, there is throughout the day it is heated and in the afternoon the pressure inside the container is 2700 millimeters of mercury, so that is p2, here are the variables we have T 1 P 1 T. 2 and P 2 and no I worry about V 1 because it remains constant here, so the equation I want will have temperature and pressure before and after, so I will use Gay Lussac's law which has P 1 T 1 P 2 and T. 2. So when you solve these problems, it can be helpful at first to figure out what your before variables are and what your after variables are.

Find out what changes and what doesn't if it doesn't change in the course of the process. equation, leave it out and then look up the gas law here that has the variables that change and that you're solving from the beginning to the end of the equation, if things don't change you're probably going to use the ideal equation. gas law, here's how to know which gas equation to choose when presented with a problem