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Learn about Junior Chemistry: Gases 3 Video
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 Learn about Junior Chemistry: Gases 3 Video
Learn about Junior Chemistry, Gases 3, in this comprehensive video by bannanaiscool.
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Rob Lederer: Charles' law is a great law because it has a wonderful application that we're going to talk about in a second. What is this law? This law is in the nutshell is that the volume and the temperature of the gas actually vary directly with one another when you keep the pressure constant. So at constant pressure, the volume of a gas varies directly with its temperature, they are directly proportional as oppose to indirectly proportional or inversely proportional as the pressure and volume were in Boyle's law. Now look at this. So V1 over T1 equals V2 over T2. So we can solve for one unknown here when we know three of the others. How do you graph something like this? Well, as one goes up, the other goes up. So you can graph it like that, right? As one goes up, the other goes up. Notice that I didn't start it here at the zero because you know what? In terms of temperature, and let's go to degrees celsius for this, okay, you can actually have zero degree celsius and you can have negative temperatures. I live in Alberta, we get negative temperatures for 11 months of the year. So if you're going to have a negative temperature, that means you can actually go into this side of the graph over here, where of this it was zero for degree celsius, you can actually go into the negatives. This is not great in terms of our calculations for this formula because if we can have zero degree celsius and we can, do we still have a volume of gas? Well, yes, at zero degree celsius, we can still breathe in Alberta and everywhere else in the world. So that means that there is still gas out there that occupies a volume. Okay, but if you put a zero in for any temperature, what you get is automatically an undefined number, it doesn't work, you can't do the math. So you're happy, right? You can't do the math. No, no, no, we have to do the math. So what we're going to do? We actually have to come up with a new temperature scale, one that incorporates all of the possible temperatures in a positive fashion. Well, interestingly in Charles' law, what he found out was you can have  this could be gas here gas X, and you could have a bunch of different gases that actually have different property, so they actually will have different volumes at different temperatures, but you know what? All of these gases will convert at one point, where theoretically they can have virtually a zero volume, all they got one point. That temperature, which hasn't really been reached yet on this planet is called absolute zero. An absolute zero is actually 0 K, for kelvins, not  no degree sign there, just K for kelvins or that's also negative 273.15 or just negative 273 degree celsius. So negative 273 degree celsius is 0 K, but fortunately celsius and kelvins go up in the same increments. So if you ever have to find kelvins, you take your degree celsius and just add 273 to get your K. Charles' law question, alright, at constant pressure because the pressure has to be held constant, 300 milliliters of the gas at 25 degree celsius is warm to 35 degree celsius, so what's going to happen? As you warm up that gas in that container, there is going to be more molecular motion that takes place, there going to be bouncing around more, but if the pressure is to stay the same, and not increase in that container, the container has to actually expand. So the volume is actually going to have to go up, if the temperature goes up. If one goes up, the other goes up in order to equal a constant K. Alright, but before you can plug numbers into that formula over there from Charles' law, you better make sure that you understand that the temperatures must be converted from 2535 degree celsius to 298 K and 308 K by adding 273. If you don't convert to kelvin, that's it, you get it wrong. No kidding, that's what's going to happen. So V1 over T1 equals V2 over T2. We got to rearrange the formula and solve for V2, that means you have to multiply each side by T2. If you do that, T2 cancels here and