actually occurring at the macroscopic level.
We've spent a lot of time so far talking about equilibrium systems.
which the macroscopic properties are not changing.
bit more about processes which are at equilibrium.
we understand what we mean by a spontaneous process.
at or the pressure that we observe.
of activity taking place at the molecular level.
In a spontaneous process the macroscopic properties.
Are changing, and they're changing in a way which is irreversible.
it's a change which is very, very difficult to reverse.
And, in addition to not being equilibrium, it's difficult to undo.
them to create an explosion in which hydrogen and oxygen produce water.
Clearly that's a significant change in the macroscopic properties.
I no longer have hydrogen and oxygen, and instead, I have H2O.
And furthermore, it's very difficult to undo that reaction.
them back into Hydrogen and Oxygen, and again.
to consider here because we're going to use them for illustrations.
Clearly as you can see on the camera over here.
I've got a deck of cards.
a nice illustration, is in fact, the shuffling in the deck of card.
through ace of diamonds, two through ace of clubs, two through ace of hearts.
And two through ace of spades.
of work to put them in this direction.
the outcome of this experiment is going to be.
well-ordered deck into a significantly disordered deck.
We now turn the cards back over again.
cards which are not in order.
discover is that I generate greater and greater disorder.
shuffled deck will require some extra intervention.
We never see that happen spontaneously during the shuffling process.
Another simple example would be the process of simply scattering things.
Scattering seeds into a field or tossing things out on the floor.
them all stacked up on top of each other or aggregate in one location.
Rather they scatter rather randomly.
I mentioned the example of mixing a little while ago.
has say, color, and one of which does not.
throughout the non colored liquid, and does so in a way which is irreversible.
the methane into into water and into carbon dioxide.
or on a cold glass of water within a high humidity area.
We see this spontaneous condensation of water on the outside of a cold glass.
and clearly is a change in macroscopic properties.
oxygen or some other oxidizing agent like water.
is extremely slow, but they're all spontaneous.
without any external intervention, and in such a way at to not be spontaneous.
why is it that some processes are spontaneous and others are not?
rust spontaneously separate into iron and oxygen.
or the rusting, to occur spontaneously, and not the reverse?
to a spontaneous process is an equilibrium process.
If things are not occurring spontaneously then we must be at equilibrium.
give us some clues as to why things come to equilibrium.
of, say, a crystal turning into a gas or a gas turning into a crystal.
are only 16 places that those four atoms might belong.
all of the pieces are near to one another.
case on the right we're going to regard that as a gas.
of which one of these is a more probable outcome.
in which we might be able to form that crystal.
There are a variety of ways.
have now contained 16 possible locations for the particles.
have put four of the particles together would include.
total of nine ways in which we can form a crystal.
With all four of the particles together.
By contrast, the number of ways in which we can form a gas is really quite large.
over the cross of the 16 different places?
Here's the total ways in which we could do that.
third, and 13 where I could put the fourth.
four particles I chose to make the first one.
one, then, which would have to be the last.
identical particles, into those sixteen locations.
1,820 ways to arrange those particles across the entire grid here.
And nine of those correspond to forming a crystal.
So correspondingly it must be that there are 1,811 ways.
In which we can form a gas.
Very significantly different there are nine ways to do this.
There are 1,811 ways to do this.
fewer ways there are to be able to produce that order.
And that begins to give us a hint as to what we want to look at.
as a means of making predictions.
did the ordered deck become the disordered deck?
have a shuffled deck when we shuffle the cards.
up with them all completely in order but it's extremely improbable.
in fact I never observe it. Even though it is in fact a possibility.
odds are only about one in 200 that that might happen.
going to observe something we would describe as a gas.
a state of low probability to a state of higher probability.
And things that happen, generally happen because they are higher in probability.
But what do we mean by the probability of a state?
if I go back to this deck of cards.
There is in fact a state in which the bottom card is the 10 of diamonds.
The next card is the three of clubs. The next card is the eight of hearts.
The next card is the two of diamonds.
the probability for arranging the cards as they were at the start of this lecture.
two through ace of clubs, and so forth.
we describe in terms of macrostates and microstates.
single card in the deck in a particular order.
There are a huge number of microstates.
the second card, all the way down to the last card.
simply a description of the macroscopic particle property.
we call shuffled, and very few ways to arrange the cards that we call ordered.
many micro states corresponding to the macro state, which is disordered.
And very few micro states.
Corresponding to the macro-state which is ordered.
Let's apply that to the idea of a collection of molecules.
The micro-state is where are each of the molecules like this.
This is a particular microstate.
They both belong to the macrostate that we call the crystal.
to the crystal is quite small.
to the gas is actually quite large.
which correspond to a particular macrostate, as we've seen here.
Don't know why that's in the way.
We then define something we'll call the entropy.
same way that W is a measure of the probability.
is very much greater than the probability of the crystal.
The way in which we define the entropy is in fact in terms of.
the number of microstates for a particular macrostate.
that corresponds to a particular arrangement in the number of particles.
The entropy is large when W is large where W is the number of microstates.
the probability will be for spontaneously choosing one of those microstates.
As in the case of the shuffled deck of cards.
from a less probable state to a more probable state, then W always increases.
This is actually going to be our first stab at the Second Law of Thermodynamics.
process, because the probability will increase in any spontaneous process.
to be a fully qualified statement of the Second Law of Thermodynamics.
that which is most probable in the universe.
and bring it into the context of chemical systems.