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In this learning objective we're going to be looking at the difference between

a standard delta G in a non-standard delta G.

Students are often don't see the nuances in the differences between these two

so I am going to try to help you work through

thinking about the difference between them. We know that this equation Delta

G equal delta

H minus T delta S would apply whether you are in standards state

conditions or not and standard state conditions.

What is the difference between standard state non-standard state? Well, let's

review what it means to be in standard state conditions.

That means that the pressures is at one atmosphere

and if it is a solution

then it will be 1 molar and when you look in tables for standard

value at thermodynamics there are usually at 25 degrees Celsius

but they don't have to be to be considered standard state.

Now, if we started out

every reactant and product in a reaction

in the standard state conditions. Lets say they are all gases and every gases was at

one atmosphere in there.

Not just to reactants, but your reactants and your products.

This system is very unlikely to be at

equilibrium under those conditions. So

if it's not an equilibrium that is going to proceed either to the right or is going to

proceed to the left. Now remember

if delta G standards is negative we know it's gonna go to the right to get

to equilibrium, it is spontaneous in the forward direction.

If standard GG is positive it's going to proceed to the

left in order to get to equilibrium.

The reverse reaction is spontaneous. Now if you wanted to know what standard delta

G at a temperature

other than 25 degrees Celsius then this is the equation that we would use.

You would look up in tables the delta H standard and the Delta S standard.

From that information these values don't change very much with temperature.

Delta G is very affected by temperature. So if you put those

standard delta H and standard delta S, even thought they are at 25 degrees Celsius.

You put in your temperature and don't forget to use Kelvins when you do so

then this is going to give you the standard delta G at a temperature

other than 25 degrees Celsius. If you needed delta G at 25 degrees Celsius

and its standard then you might as well just go to the tables and determine the standard

delta G for the reaction

and not use this equation. So we have a series of questions that I want you think

through in order to figure out

the connections between what is delta G standard telling you

and how does it change when you leave standard state conditions.

So I have a reaction and in this reaction chamber I'm starting with

every gas at one atmosphere.

So that's what's being represented in that picture. That is a standard a condition.

We see here that the standard delta G is a negative value

a -190.5. So if I started everything out at one atmosphere which

statement would be true?

Would the reaction shift to the right to get equilibrium, or shift to the left to get equilibrium,

or neither, it is already an equilibrium?

If you said A you would be correct.

A negative value for a standard delta G says,

and this is all it says, it is snapshots that says, if we started

everything at at 1 atmosphere this reaction would proceed

to the right because it's negative. Let's again start this system out at equilibrium.

I mean start the system out with everything in its standard state

conditions with 1 atmosphere.

So we're here. We know according to this standard delta G that if we start

everything and a standard state conditions

the reaction will proceed to the right. Now if it gonna proceed to the right.

What is going to happen to the pressure HCl?

Well if you said it will increase

you would be correct. The HC; pressure is going to go up.

These pressures are going to go down as it proceeds to the right.

So it's always going in the forward direction and reverse reaction are always happening

but more of the forward is happening then the reverse when you have a -190.5

kilojoule, we have a negative value for that standard delta G. Now as soon as it

starts proceeding to the right

my question for you is, is it still under standard state conditions?

Well no, because if the pressure is going up it is no longer one atmosphere

it is greater than one atmosphere. And if its greater than one atmosphere

then we are not under standard state conditions and this number

of - 190.5 no longer applies. It

only applies when when we are in standard state conditions.

Just to think about this,

does it really give us a good connection between standard and non-standard delay G?

What's going to happen to the total pressure on the system

as you establish equilibrium from the point

at the beginning where everything is one. Starts proceeding to the right

and it finally get equilibrium and the foreign reverse and reaction are happening at the

same rate, what is going to happen to the total pressure?

If you said stay the same, then you're correct? The pressure of

HCl is going up as it proceeds to the right. The pressure of H_2 is going down

the pressure Cl_2 is going down

because the number of moles on the left which we have two moles and gas not just

is not just moles its moles and gas

there's two moles gas in the left and there's two moles a guess on the right

then as this reaction shifts the total pressures not changing.

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and it finally gets there. Once it

establishes equilibrium what is going to be the value

of the standard delta G. Will it increase to get equilibrium?

Will it have decreased to get to equilibrium? Or will it stay the same?

Students often miss this.

So don't feel bad if you didn't you've got to get to the

understanding of why would stay the same. A standard delta G

is a snapshot of where where it would be

if everything were at one atmosphere. So standard delta G never changes.

Its value is the - 190.5 kilojoules per mole for this reaction.

So as a reaction release these one atmosphere conditions

we no longer have a standard state condition

but the standard delta G is the snapshot of what it is when everything is that.

So don't think that your standard delta G is going to change.

Which Delta G without the circle

it certainly will change. So our next question is to think about

what is happening to Delta G. Once

you establish equilibria. Will it be positive will be negative?

Will be equal to 0. Well it you said it would be equal to 0 you are correct and that's exactly what happens.

Delta G equals zero an equilibrium.

Not standard delta G the only way

standard delta G could equal 0

is if when everything was that was at one atmosphere

this thing happened to be at equilibrium. Very, very unlikely.

Very unlikely. Well this reaction certainly isn't it had a negative value

we know it wi'll proceed to the right. We will build up more and more

of these two. We will use up some of this and some this and finally get to equilibrium.

When he gets the equilibrium, at that point

the Delta G for the reaction is no longer standard state conditions

is 0, That is true for every reaction it's Delta G is equal to 0

at equilibrium. So what happened to the Delta G?

The Delta G started out when we were all at one atmosphere

with this number. It gets to equilibrium

Delta G non-standard is equal to 0

so the negative Delta G is increasing

as the reaction keeps working its way closer and closer

to equilibrium. Now we will look at the mathematical relationship between the standard

in a non-standard delta G, there is a connection. So anytime you need in

non-standard delta G

is when you're not in standard state conditions.

We have this equation help us get to a non-standard.

So if we want to know what the reaction was at

going to proceed to the right or proceed to the left and we had conditions other than

standard state conditions

then this is the equation that we would use. The R that we use in this equation

is the 8.314 because it has the

energy unit a joule, and you actually probably have to convert it to

kilojoules before you could add those terms together.

We see that a Kelvin is here in this K and that's what we have to use for the temperature

and our Q is a reaction quotient.

The reaction quotient if we remember for reaction is just like a K

equilibrium constant. Its products and concentrations if there aqueous

pressures if it is

gases, but its products over reactants

raised to the power of their coefficients. So there's some coefficients of the

balanced equation is raised to those powers.

So that's what the reaction quotient is so

we can look at this reaction and say OK at this point in time

there is this much product, there is this much reactant. Let's put those numbers in there

and let obtain a value for a non-standard

delta G. Now if everything were 1 then Q would be 1.

And if Q is one the natural log of Q is 0 and this term goes away

and that make sense.

So we're just gonna think through this equation.

In terms of what how does change in Q affect the Delta G?

So let's start with a standard Delta G that's negative.

This means that the reaction is spontaneous in the forward direction.

if you we in standard state conditions. We put everything in a

reaction chamber

and this is kinda like our little questions that we went through

are standard delta G was negative the reaction spontaneous in the forward direction.

So the question is what would happen, we have to do, in terms of conditions?

What would we have to do in terms of Q here in order to make Delta G positive?

Well if the delta G is positive we know that it's no longer spontaneous in the forward

direction is now spontaneous the reverse direction.

How do we make Delta G positive? Well, the only way we can make delta G positive

is to make this term positive.

Well this term is positive when Q is what? How do we make the natural log of Q

be positive value? Well

if Q is greater than one

it's a value that is bigger than one then the national log of Q is positive.

That is the first thing. As long as Q is greater than 1 then when we take the natural

log it will be positive in this term

that I have circled up there is going to be a positive term. We just gotta make

positive enough.

So anytime that the products are greater than the reactants because remember what Q is?

It is products over reactants.

Remember? Raised to the power of their coefficients.

So anytime products is greater than reactants

then the Q is going to be bigger than 1 and a national log of Q will be a

positive value

and we can get it positive enough to overcome all the negative that we have here.

We can turn a reaction that was spontaneous in the forward

direction to be spontaneous instead

in the reverse direction. Well lets go through that same mathematical logic

in the revers. What if the standard up to G was positive

the reaction is not spontaneous in the forward direction

it is only spontaneous in reverse reaction direction

if everything were under standard state conditions.

So we start everything is standard state conditions. We know the reactions going to proceed

to the left. That is when a positive

means its spontaneous in the reverse direction.

What conditions would we have to have in order to make

this negative. We want this reaction proceed in the forward direction

instead of in the reverse direction. Well lets think about what has to happen to this term.

In order to make this reaction becomes spontaineous the forward direction

this term is going to have to be very negative. It is going to have to be negative enough to

overtake the positive of the standard delta G.

How can we make that term negative?

Well, the only way we can affect that term R cannot change it's always the same.

Temperature is Kelvin and there's no such thing as a negative Kelvin so the only

way we can make this term negative

is to make the natural log of Q negative.

So if Q is less than one, it is a fraction

less than 1. Then anything can you take the natural log of a number less than 1

its negative. So how do we make Q less than one?

Once again we remember that Q is products

over reactants raised to the power their coefficients.

As long as you have a lot of products so this is a big number.

and this is a small number. So products

is an smaller than the reactants and you want to have a number

less than 1 and as long as it is small enough

this natural log of Q would be negative enough that we would

have more negative than we have positive and that would make my

non-standard delta D negative and we can for force this reaction to become spontaneous

in the forward direction. Now you going to

be doing mathematics numbers for this it's not a big deal.

You just gotta watch for signs if you're given a standard delta G

and they want to know a non-standard delta G this is the equation you will pull out.

Watch you units if Delta G which is typically in kilojoules is given to you

and then we're going to have to make sure that this term gets converted

kilojoules before we convert it.

The thing you have to watch is your T and make sure it is in Kelvin.

Then you will be able to easily convert between a standard delta G

and a non-standard delta G.

So this is the enough are learning objective number 9 in which we are

seeing the connection between the Standard delta G and a non-standard delta G.

We see that they're not the same thing we have to understand their differences

and we have an equation that will help us

convert between them.