Name: 應用理想氣體定律(PV=nRT)的例子。 (Applying ideal gas law (PV=nRT) example)
Uploaded: 2021-01-14T10:53:19.000Z
Duration: 7 min 17 s
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- [Instructor] We're told an athlete takes a deep breath,

and see if you can figure this out on your own.

All right, now let's work through this together.

So let's think about what they are giving us

So, they are giving us a volume, right over here.

They are also giving us a temperature, right over here.

And they want us to figure out the number of moles.

And so, do we know something that connects pressure,

temperature, volume, and the number of moles?

Well, you might be thinking of the Ideal Gas Law,

And so we know everything here except for n,

And it's going to be dependent on which units we use,

and we'll figure out which version of R we use.

But that's why I gave you this little table here,

if you were taking something like an AP exam.

So, to solve for n, you just divide both sides by RT,

And so this is going to be equal to what?

Well, our pressure is 754 millimeters of mercury.

Now, over here, where they give us the ideal gas

or the different versions of the ideal gas constants,

But for the purposes of a first-year chemistry class,

you can view a millimeter of mercury as being a Torr.

So, you can view the pressure here as 754 Torr.

And then we're going to multiply that times the volume.

and we're probably going to be using this one,

that has liters, Torr, moles, and Kelvin.

I'll use this version because it's using all

"Wait, the temperature's given in degrees Celsius."

But it's easy to convert from degrees Celsius to Kelvin.

to whatever you have in degrees Celsius to get to Kelvin,

because none of these are given in degrees Celsius.

And so, I will use this ideal gas constant.

Mole to the negative one is just one over mole,

Kelvin to the negative one is just one over Kelvin.

And then, I'm gonna multiply that times the temperature.

So times, what is 21 degrees Celsius in terms of Kelvin?

Well, I add 273 to that, so that's going to be 294 Kelvin.

And we can validate that the units all work out.

This Kelvin cancels out with this Kelvin.

And so, we're going to be left with some calculation.

And, it's going to be one over one over moles,

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應用理想氣體定律(PV=nRT)的例子。 (Applying ideal gas law (PV=nRT) example)

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