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AP Chemistry 3.5 Chemical Reaction Rates 7 Views


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Description:

AP Chemistry 3.5 Chemical Reaction Rates. How much 85 Kr will we need to collect?

Language:
English Language

Transcript

00:03

Here’s your Shmoop du jour, brought to you by world domination.

00:08

How hard is that to pull off, anyway? [Man dressed in battle gear preparing a plan for world domination]

00:09

…We’re asking for a friend.

00:12

Here’s today’s question:

00:13

As evil masterminds, we are on the verge of learning how to make kryptonite so that we

00:17

can render Superman powerless. [Krptonite and Superman appears]

00:19

We learn that we need 18 g of a radioactive isotope of krypton, krypton 85, to complete

00:25

our recipe for world domination.

00:28

Krypton 85 has a half-life, t one half, of about 10 years, and it only exists on the

00:34

planet Neptune.

00:35

It will take us 20 years to return from Neptune back to Earth.

00:39

How much krypton 85 will we need to collect from Neptune to have enough left to take over the world?

00:48

And here are your potential answers:

00:52

Superman is strong, fast, and pretty darn handsome, but even he can be defeated by a [Superman makes robbers disappear]

00:57

chemical compound. [Masked man shows Superman kryptonite]

00:58

So you can feel better about AP Chem being your one weakness.

01:01

You’re in good company.

01:02

To solve today’s problem, we need to remember that the half-life is the amount of time it

01:06

takes for half of the radioactive compound krypton 85 to decay.

01:11

After each half-life passes, the amount of krypton 85 left has decreased by a factor

01:16

of two.

01:18

Not to be mixed up with the time period “half of your life,” which is how long we were [Man sat waiting at a table]

01:22

waiting for Adele to release her new album. [Adele singing]

01:25

No hard feelings, Adele.

01:26

It was worth the wait.

01:28

Anyway, the half-life of krypton 85 is 10 years, but the journey back from the planet

01:33

Neptune will take 20 years.

01:35

It will also take us 20 years to get to Neptune…

01:38

Forty years is a perfectly reasonable amount of time to take to surprise somebody, right? [Superman grows a beard]

01:44

Nobody can catch on when you’re moving that quickly!

01:46

So the 20 year journey home is equal to two half-lives of Krypton 85.

01:53

During this time, the amount of krypton 85 will be cut in half twice, so the amount remaining [Masked man holding krypton]

01:58

when we get back to Earth will be only one quarter of the amount we had when we left

02:03

Neptune.

02:04

We’ll have to gather exactly four times as much as we need, but absolutely no more. [A small and large piece of krypton]

02:09

We might be evil, but we don’t have to be wasteful. [Masked man drops soda can in the trash]

02:11

Since we’ll need 18 grams of krypton 85 on earth, and we have to gather four times

02:16

as much on Neptune, that means we have to collect 4 x 18 = 72 grams.

02:23

That means D is the correct answer.

02:25

Now all that’s left is to execute our brilliant secret plan.

02:29

Good thing Superman doesn’t watch Shmoop. [Superman watching Shmoop on TV]

02:31

Or does he…? Dang it.

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