Brief Summary
In this video, Dr. B explains the combined gas law, detailing when to use it, and how to ensure unit consistency while performing calculations. He covers examples involving initial and final conditions of pressure, volume, and temperature, emphasizing the importance of working in Kelvin and using equivalent pressure units.
- The combined gas law applies when there are changes in initial and final conditions.
- Always convert Celsius to Kelvin and ensure pressure units match.
Dr. B introduces the combined gas law, explaining its application in problems involving initial and final conditions of gases. He starts with an example, using an initial volume of 2.3 liters and a pressure increase to 4.7 ATM, where the temperature remains constant, simplifying calculations to Boyle's Law. After setting up the formula, he finds the final volume to be 0.64 liters.
The next example requires finding volume after cooling at a new temperature. Dr. B stresses converting from Celsius to Kelvin by adding 273 to the Celsius value, a crucial step for accuracy. For this scenario, he calculates the final volume as 3.13 liters after correctly setting up the formula with Kelvin values.
In another example, Dr. B highlights the importance of using the same units for pressure, converting mmHg to atmospheres by dividing by 760. After ensuring the units are consistent, he calculates the final volume, resulting in 8.6 liters. This section reinforces the necessity of unit conversion to maintain accuracy in calculations.
Dr. B wraps up the video with a recap of using the combined gas law effectively. He emphasizes the critical steps of converting temperatures to Kelvin and ensuring that pressure units are compatible, all pivotal for obtaining correct results in gas law calculations.
Summarize any YouTube video in seconds
Get summaries like this one for any video, in your language, with the free Summ app.
Transcript
Full transcript of “Combined Gas Law: Explanation, Practice, and Examples”. Click a timestamp to open the video at that moment. Need another video? Use the YouTube transcript generator.
0:01 so in this video we're going to look at the combined gas law and you're going to learn when to use the combined gas law how to make sure your units are the same on both sides and then how to do the math correctly so let's get started so first off when do you use the combined gas law here's the thing you're looking for initial and final conditions so in this problem we start out with 2.3 l we have a pressure of 1.3 ATM and they ask what is the volume when the pressure is increased to 4.7 ATM so the pressure it changed we have an initial pressure right here and then a final so we're going to use the combined gas law so in this case we're told that temperature remains constant so we can just ignore the temperature right here and now we just have boils law so let's put the numbers in we have our initial pressure our initial volume here's our final pressure pressure and we're solving for v2 so to get V2 here by itself let's divide both sides by 4.7
1:07 ATM so now this cancels out and we're left with V2 so over here we have atmospheres in the numerator and denominator cross them out we're going to be left with liters and that's what we're looking for that's volume so we know we set this up right multiply the top and then divide by the bottom that gives us V2 we end up with 0 .64 l so remember when something's held constant we can just take it out of our combined gas law let's do another one so pause and see which equation you need to use for this one so I can see I have volume and then a temperature and we want to know what the volume is after it cools afterwards this new temperature we have initial and final combined gas law so pause again and see if you can solve this one but there's something we want to watch out for we have our temperature it's in Celsius we really want to work in kelvin sometimes it works if you use celsius but it's best to be in kelvin so to do that we take the degrees Celsius add it to 273
2:20 that'll give us Kelvin so I'll do that for both of these here so you always want to be working in kelvin with both the ideal gas law and the combined gas law all right now pause see if you can solve this problem here so they say the pressure remains constant let's just get rid of that so we just need to put these variables in so we're solving for v2 let's multiply both sides by 288.15 and this will cancel out here giving us V2 by itself over here Kelvin cancels out left with liters that's what we're looking for multiply divide we end up with 3.13 L so make sure you're working in kelvin when you're doing any of the gas laws okay let's do another all right pause and give this
3:20 one a try just try to set it up then we'll come back and talk about it before we solve it so we have initial conditions and final we're going to use the combined gas law but we have Celsius we want to get that to Kelvin and then pressure we have one atmosphere and then mmhg that's the new pressure these have to be in the same units so let's first convert this over to let's make it atmospheres here's how you do it essentially we're dividing this number by 760 mm of mercury it's because one atmosphere is 760 mm of mercury that's a conversion factor fact so we multiply this cancels out we divide this by this we get 2.08 atmospheres so now these are the same let's write this up here for the temperature since it's in Celsius we add 273.15 we get so now all the units are the same and that's really important we plug it into our equation and now I'll work to get V2 by itself multip both sides by this so it'll cancel out over here divide both sides by this so it cancels out on this
4:37 side we have V2 by itself multiply everything here and then here then divide this numerator by the denominator you end up with 8.6 l so again make sure everything works out to be the same with the units and you'll be good this is Dr B looking at some examples and explanations about the combined gas law thanks for watching
