Thermodynamic meaning of molar Gibbs free energy

[Legnal]

What's the thermodynamic meaning of these molar Gibbs free energy values? I know that when it is ΔG>0 , it means there is no spontaneity, when   ΔG=0 there is equilibrium, and when  ΔG<0, there is spontaneity. But what happens when G is molar? 

Edited November 20, 2020 by Legnal

[studiot]

This is in homework help.  So I can't answer the question directly  -  is this really a homework question or are you actually seeking an explanation ?

Also you have asked for the 'thermodynamic meaning'  - whatever that is.

Thermodynamically, working 'per mole'  is a method of quantifying that is very convenient, particularly in Chemistry.
In Physics and Engineering quantitative calculations are often carried out 'per kg' or even 'per container full'

But in Electrochemistry we obtain the full benefit of working 'per mole' since 1 mole of charge is 1 coulomb of electricity.

So per mole units can be directly converted to the Electrochemistry of cells, half cells and even reactions via the Nernst equation, Faraday's Laws etc.

Please tell us more about the background to this question.

 

[joigus]

Gibbs free energy, roughly speaking, means the energy stored in all the chemical bonds. The \( \triangle \) quantity means difference between products and reactants, and 'molar' means 'per mole' or 'per molecule'.

x-posted with Studiot.

Edited November 20, 2020 by joigus

[studiot]

19 minutes ago, joigus said:

 roughly speaking, means the energy stored in all the chemical bonds

Isn't that the Enthalpy ?

'Free energy' includes an entropic contribution.

Edited November 20, 2020 by studiot

[joigus]

2 minutes ago, studiot said:

Isn't that the Enthalpy ?

'Free energy' includes an entropic contribution.

You're quite right. There is a caloric part in \( G \) that is usable for doing work. Thank you.

[Legnal]

4 hours ago, studiot said:

This is in homework help.  So I can't answer the question directly  -  is this really a homework question or are you actually seeking an explanation? 

Yes, this is a homework question. 

I'm pretty sure the answer is related to equilirium and spontaneity, becuause my teacher always rembembered us those 3 values of ΔG and their meaning. But now that ΔG  is molar, i'm not sure what happens with the equilibrium and spontaneity.

[studiot]

11 minutes ago, Legnal said:

Yes, this is a homework question. 

I'm pretty sure the answer is related to equilirium and spontaneity, becuause my teacher always rembembered us those 3 values of ΔG and their meaning. But now that ΔG  is molar, i'm not sure what happens with the equilibrium and spontaneity.

Thank you.

Yes, you are correct the change in Gibbs free energy tell us whether a process (including a chemical reaction) is thermodynamically feasible without outside assistance. (ie spontaneity)

But the statement of any form of energy, internal energy, heat energy, specific heat, work etc is meaningless without relating it to to something. There is twice as much energy in 2kg or 2 moles  of something as in 1kg or 1 mole.

So relating it to the number of moles makes no difference to its significance to this fact.

You have correctly identified that delta G has to be negative for a reaction to be able proceed of its own accord,

A good answer would include the meaning of the negative sign.

A very good answer would include a note as to whether this means the reaction would necessarily proceed or if any other factor might be involved.

 

Does this help ?

 

[Legnal]

3 hours ago, studiot said:

But the statement of any form of energy, internal energy, heat energy, specific heat, work etc is meaningless without relating it to to something. There is twice as much energy in 2kg or 2 moles  of something as in 1kg or 1 mole.

I forgot to mention, this is in the context of partial molar properties, so i suppose this molar ΔG is referred to a solution. Right? In that case, is it a change due to mixture?

[studiot]

Partial molar quantities can also be represented by partial pressures.

The truth is that for extensive properties ( do you understand this term ?) like volume, mass, energy, entropy the partial (or specific) properties are additive.

So specific volume, molar volume, specific energy etc are additive.

Such properties are all represented by an overbar.

Since you are doing this in relation to partial properties are you doing the calculus of this ?

I'm sorry, I missed the molar bit first time round.

Edited November 21, 2020 by studiot