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Grumpy Professor Hank admits to being wrong about how everything is chemicals. But he now wants you to listen as he blows your mind with a new sweeping statement: everything (yes, really everything this time) is energy. What?!
This week, Hank takes us on a quick tour of how thermodynamics is applied in chemistry using his toy trebuchet as an example, because he is a proud nerd.
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Transcript Provided by YouTube:
00:00
I have a certain fondness for saying everything is chemicals,
00:03
mostly this is because I’m tired of all the people complaining about all the “chemicals”
00:07
that they are exposed to when literally everything you have ever been exposed to,
00:12
including the most organically grown lettuce is composed entirely of chemicals.
00:16
But when I say everything is chemicals, I am in fact wrong.
00:20
There are quite a lot of things that aren’t chemicals:
00:22
sound, heat, laser beams, the existential concept of selfness…rainbows.
00:26
All of those things are things.
00:28
And all of the things and also all other things are, in fact
00:32
— oh god this is weird but it’s true — they’re all the same thing: energy.
00:37
Everything is energy.
00:39
[Theme Music]
00:48
Let’s talk about trebuchets.
00:50
The trebuchet was a weapon of war,
00:52
but it is also a feat of ancient engineering so I remember it for that instead of for all the people it killed.
00:58
Well, I happen to have a very small one that I built from a kit, because I’m a nerd.
01:03
This tiny trebuchet contains quite a lot of energy.
01:05
In fact, more than you might suspect.
01:07
And because we are humans and we like to understand stuff,
01:09
we shall put the energy it contains into a bunch of different boxes.
01:13
Let’s start with the least obvious one: its mass, since, as Einstein told us, energy and mass are the same thing.
01:18
Now we’re not gonna go into detail there,
01:20
instead we’ll just say that the energy is well and locked up and extremely difficult to access
01:25
because the nuclear energy of the wood is not easy to release.
01:28
Which is excellent, because the nuclear energy of this trebuchet, if released,
01:32
could destroy the entire building that I’m sitting in.
01:34
This little war machine also has thermal energy;
01:37
anything warmer than absolute zero has thermal energy, even very very cold things.
01:42
This basically means that all of the individual atoms and molecules are jiggling imperceptibly.
01:47
Only at absolute zero would they stop jiggling.
01:49
If I were to touch it then my hand would instantly freeze and then fall off of me.
01:53
Absolute zero is very cold.
01:55
It also has chemical energy, which is stored in the bonds between the atoms.
01:59
All of the bonds in the molecules of cellulose and lignin that make up the wood contain energy,
02:04
and some of them could be broken, releasing that energy,
02:06
which is what would happen if I lit my trebuchet on fire,
02:08
which I will not do because it took like four hours to put together.
02:11
Now none of those forms of energy are the forms of energy that the ancient generals were interested in,
02:14
of course, but I wanted to illustrate how much energy really is in there.
02:19
What the ancient generals were interested in was the system’s gravitational potential energy,
02:23
because this heavy thing here which is full of pennies
02:26
— oh God, that’s dangerous —
02:27
this thing is heavy, it’s full of pennies, and it has been lifted up, and the force of
02:30
gravity is trying to pull it back down.
02:33
This stored gravitational energy is a form of potential energy;
02:36
that is, energy contained within a system because of its position.
02:39
This does not mean that it has the potential to become energy.
02:42
It is energy. It’s just stored.
02:46
If it wasn’t there, and then it was, then you would be creating energy.
02:49
And as we all know, you cannot create energy.
02:52
Like, we all do know that, right?
02:54
It’s the first law of thermodynamics, also known as the law of conservation of energy,
02:58
which is a real, hard and fast, not just unbreakable but unbendable law of physics.
03:04
Energy cannot be created and it cannot be destroyed.
03:06
The amount of energy in the universe is constant.
03:10
And since everything is energy, the amount of everything in the universe is constant, which is a little bit trippy.
03:15
Deep thoughts like that one are what formalized the study of energy into what we call thermodynamics,
03:21
the branch of science studying heat, energy, and the ability of that energy to do work.
03:25
Okay, now I just said three words that you think you know the definition of but you probably don’t.
03:29
That’s okay, you’re gonna be wrong many times in your life, this is just one of them.
03:34
So, what were those words?
03:36
Energy. I know that you don’t know what energy is, because, like, I don’t either.
03:40
Nobel Prize-winning physicist Richard Feynman said:
03:42
“it is important to realize that in physics today we have no knowledge of what energy is.”
03:46
But let’s just give the same cop-out answer that my textbook gives, which is:
03:49
“the capacity to do work or produce heat.”
03:52
Work. In the common vernacular, that’s anything that you have to do but you don’t want to.
03:56
But in physics and chemistry, work is when a force acts on something, causing it to move.
04:00
If nothing moves, then no work is done.
04:03
There are a few different symbols that represent work, we’re going to use the lowercase “w.”
04:06
Heat. Which is maybe the most misunderstood word in chemistry after the word chemicals.
04:09
Heat is not something that objects contain.
04:12
Just like something can’t have work, something can’t have heat.
04:15
Instead, heat, just like work, is an energy transfer.
04:18
But instead of transferring energy by mechanical movement,
04:20
heat is a transfer of energy by thermal interactions, such as radiation or thermal conduction.
04:25
Now crazy as this might seem, those are the only two things that energy can do.
04:28
It can either be work applying force and moving things or it can be exchanged as heat.
04:33
Both process result in an energy transfer between systems.
04:36
And just in case you weren’t confused enough, the most common symbol for heat is lowercase “q.”
04:41
Yup. Lowercase “q,” deal with it.
04:44
Little-known fact: the word “heat” used to start with a silent q,
04:48
but it was dropped in the seventeenth century when — I’m just making stuff up.
04:51
So we’re just gonna have to move on, leave that behind us,
04:53
and think about what happens when the amount of energy in a system changes.
04:56
If you’re currently freaking out, thinking, like, “but Hank, you just said that the amount of energy never changes!”
05:02
I will remind you that I said “in the universe.”
05:04
See, when we’re doing thermo, we get to divide the universe into two parts,
05:07
which is actually a pretty cool thing to get to do.
05:08
One part is the system, the thing that we’re studying, and everything else is the surroundings.
05:13
The surroundings allow the amount of energy in the system to change.
05:17
That change just has to come from or go to the surroundings.
05:21
And we get to decide where that line is.
05:22
We could say that the system is the rock that the trebuchet propels, or the sling,
05:26
or the trebuchet itself, or the face of the poor guy that the rock runs into.
05:30
Whether it’s the Earth-trebuchet system, or the rock-face system, or the entire observable universe system,
05:35
we get to decide based on what we’re interested in studying.
05:38
Every system has an internal energy, the sum of all that system’s kinetic and potential energy.
05:44
The internal energy of the system is represented by a capital “E”,
05:47
and usually we’re interested in changes in that system.
05:50
And the way we represent change in chemistry and physics is with the Greek letter delta(Δ),
05:53
so we stick the delta in front of the “E” for “ΔE”, the change in the energy of the system.
05:58
The change in the energy of the system is equal to the heat plus the work.
06:01
The simplest equation you’re ever gonna see on Crash Course Chemistry.
06:04
There are two basic outcomes when you’re looking at this internal energy equation.
06:07
The first is that ΔE is positive. It’s gaining energy from the surroundings.
06:11
That’s the case if work is done on the system or heat is transferred to the system.
06:15
Like if I were to do some work to get the trebuchet ready to fire, ΔE is positive.
06:20
The system is gaining energy from its surroundings, which includes my arms and muscles.
06:25
If work is done by the system or heat is transferred from the system to the surroundings,
06:29
those w and q get negative signs resulting in a decrease in ΔE,
06:34
or a loss of energy from the system to the surroundings.
06:36
Like when the trebuchet fires, the trebuchet’s ΔE is negative from the transfer of energy to the ping pong ball.
06:43
So what in the name of Willard Gibbs does any of this have to do with chemistry?
06:47
Well, the energy stored in molecular bonds, chemical energy, is a kind of potential energy.
06:52
It exists because of the position of the particles in the molecule.
06:55
Just like with the trebuchet, in chemistry we can put energy into molecules, and take
06:59
it out, and even use it to do work,
07:02
creating war machines millions of times more powerful than the biggest siege engine ever constructed,
07:06
but also creating tools to feed and clothe the world.
07:09
Some reactions release energy, like if I lit my trebuchet on fire — which again I will not do!
07:14
Why do I keep bringing that up!?
07:15
Burning is the rapid oxidation of chemical compounds,
07:18
and as it results in a heat flow out of the system we call that an exothermic reaction.
07:22
But other reactions suck energy out of the environment and into the system.
07:26
These endothermic reactions occur when heat flows into the system.
07:30
Like in your car engine, at the high temperatures of combusting fuel,
07:33
Nitrogen and Oxygen will suck some of that energy into chemical bonds forming nitric oxide,
07:37
a poisonous gas that I once inhaled a dangerous amount of, but I’ll save that story for our lab safety episode.
07:43
Chemistry, it turns out, is largely a study of energy.
07:47
The energy stored in bonds, transferred between atoms and molecules to find stable forms and released to the environment to do work.
07:54
It’s just like the trebuchet:
07:55
put energy in, store it, and then take it back out to do something interesting, fun or useful.
08:00
That’s basically everything that ever happens summed up in one little siege engine. Not bad.
08:06
Thanks for watching this episode of Crash Course Chemistry.
08:08
If you were paying attention, you learned that everything is energy;
08:11
that there are lots of different forms of energy including potential energy,
08:15
which is energy contained within a system because of the position or arrangement of its components.
08:20
And you learned that chemical energy is a kind of potential energy, energy stored up in bonds between atoms.
08:25
Also you hopefully already knew that energy can neither be created nor destroyed,
08:28
and that the amount of energy in the universe is constant;
08:31
but when studying thermodynamics we divide the universe into the system and its surroundings,
08:35
and a system could give energy to or take energy out of those surroundings.
08:40
You learned that energy can be transferred in two ways: work, which is force applied over a distance,
08:44
and heat, which is the transfer of energy by thermal interaction.
08:48
And finally, you learned that all of this is just as applicable to chemistry as it is to trebuchets.
08:53
This episode was written by Kim Krieger and myself, edited by Blake de Pastino,
08:57
and our chemistry consultants were Dr. Heiko Langner and Edi Gonzalez.
09:00
This episode was filmed, edited and directed by Nicholas Jenkins, our script supervisor was Caitlin Hofmeister,
09:05
Michael Aranda did the sound design and our graphics team is Thought Café.
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This post was previously published on YouTube.
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Photo credit: Screenshot from video
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