ΔGstandard, ΔGshmandard

Last time I made a bit of a mess of things trying to talk about them...Let's maybe not be messy tonight.
I need to finish talking about chapter three so I can move onto four and five. Some of the pictures have not been loading and I think that's just cause I've been copy and pasting them and maybe this site doesn't like that, so tonight I'll try to go through imgur.

When you've got a reaction and you are talking about which direction it's going to be favored to go in, you use terms like enthalpy (the energy of a reaction) and entropy (randomness of things that are happening, freedom of molecules, etc). 

The formula ΔG=ΔH-TΔS allow us to calculate the ΔG "Free Energy" of a system, which is in turn going to tell is if a reaction will be favored or if the reverse of a reaction is favored. Typically, reactions that are ΔG- are favored to go forward and if a reaction is ΔG+, the reverse of the reaction is favored. And all THAT depends on the interplay of entropy and enthalpy (TΔS and ΔH)

So when we take the first reaction in the book, fermenting glucose to ethanol, we see that ΔH is -82kj/mol.

Let's remember how messy we were last time. 

The reaction Glucose ---> Ethanol is ΔG - 218kj/mol

The enthalpy is strongly negative value, which is good for ΔG

The entropy happens to also be a negative value, which is good for ΔG

So ΔG gets to be negative and the reaction proceeds in that direction.

Thanks to Lenny, I can finally understand the term "kinetically stable" (metastable). It's used to describe something that is stable and not going to be torn apart by hydrolysis...at the moment. The nucleic acids chapter talks about how DNA is metastable. Eventually that shit will get hydrolyzed and we'll get broken down and things are going to eat us apart...but not yet. Kinetics deals with rates, and that's something we can't get ΔG tangled up in. Page 67, the textbook says: "The favorability of a process has nothing to do with its rate" and goes on to say that large negative free energy doesn't mean that it's going to happen fast....but it IS going to happen. 

ΔG's sign tells us if a process (or process's reverse reaction) is favored

ΔG's magnitude tells us how far the process is from being at equilibrium

ΔG also tells us how much useful work we can get out of something...it can sort of tell us if a process is going to happen, for what it's going to be used. Sort of. 

A different way to talk about this shit explains how the ΔG of a system depends on the concentrations of products/reactants you got going in a reaction.

That beast.

The book plays a game called not defining ΔGs (ΔG standard, too hard to find a way to put a degree sign as I keep just copy & pasting the Δ) until the next section, so we can play along.

This equation is supposed to give us the energy to do work from a reaction that happens. 

The next part is Chemical Potential. 

We start off by talking about the relationship between ΔG and what crap you have in your "flask". The chemical potential of a thing you have is the measure of what it contributes to the ΔG of the system. 

When they say "state function" they mean it depends on the initial and final states for what is going on in your reaction. 

Let's take this for example, something the book talks about

You've got two solutions of stuff that's separated by something through which stuff can pass.

Let's say this is what you have on Monday. On Monday, there's lots of stuff in area one, we call the concentration A1. There's less stuff in Area 2, we call the concentration of that stuff A2. Then you wait until Tuesday, for some of the stuff to move into the "bottom" region. The direction that the stuff is going to move in is going to help us evaluate ΔG

Alright. Now it's Tuesday, and our stuff has moved. Now we have about the same amount of stuff in both regions. 

When we're looking at the two days individually, we can compare their free energies with the formula from before, one formula per day, and then use the concept something being a state function and dependent on the final (tuesday) and initial (monday) states, apply all that to the formula. When the ΔGs values cancel out and you know how to use log/ln properties, we're left with:

ΔG = RT ln ([A1]/[A2])

This formula is pretty fucking important.

If the concentration of A2 is less than the concentration of A1, ΔG is going to be negative, meaning all the stuff that was transferred was favorable. 

If, however, the concentration of A2 is more than the concentration of A1, ΔG is going to be positive, meaning the movement of stuff is unfavorable into the "lower region" but the movement of stuff out of there IS favorable.

If the two concentrations are equal, ΔG is zero meaning the system is at equilibrium (which is actually what's going on Tuesday)

If some stuff can pass through a "membrane", the direction that is it going to want to go is going to be from a place with LOTS of stuff to a place with NOT SO MUCH stuff. It's going to go from a place where the chemical potential of stuff is high to a place where chemical potential of stuff is low. This chemical potential is the driving force behind this. It's going to move the system toward equilibrium, where the concentrations of stuff on both sides of the "membrane" are equal and there will be no more driving force since ΔG will be zero. 

In situations where stuff happily goes the reverse way, from LOW concentration to HIGH concentration, there will be a free energy price to pay and we can pay it by "coupling" this movement of stuff to some type of reaction that is thermodynamically favorable. The book says: "Two or more reactions are coupled when one reaction cannot occur without the other reaction also occurring"

We can wiggle around that last ΔG formula

ΔG = RT ln ([A1]/[A2])

And change it so that it reflects a reaction that is occurring with products and reactants and shit.

The terms Q and K become sort of interchangeable and it is basically the equilibrium constant for the reaction...the concentrations of Products/concentrations of reactants such that, for a reaction AT equilibrium, where ΔG = 0....

ΔG = ΔGs + RT ln (Procuts/Reactants)eq = 0

0 = ΔGs + RT ln (Products/Reactants)eq (and we can move ΔGs to the other side to make..)

-ΔGs = RT ln K

The book calls ΔGs a "reference value for free energy change" ... you compare the free energy changes in reactions under equilibrium circumstances. 

All of THIS and especially reaction coupling is what's going to get me into the next post. Using real worlds. Not Monday and Tuesday worlds.