Gibbs free energy- entropy Watch

Aaradhana
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The book says, "While change in enthalpy is a measure of the quantity of heat change during a chemical reaction, Gibbs free energy gives a measure of the quality of the energy available"... What?

How is Gibbs free energy a measure of the quality of the energy available? I really don't get it.
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username913907
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(Original post by Aaradhana)
The book says, "While change in enthalpy is a measure of the quantity of heat change during a chemical reaction, Gibbs free energy gives a measure of the quality of the energy available"... What?

How is Gibbs free energy a measure of the quality of the energy available? I really don't get it.
It's a measure of the energy available.... why is this harder than enthalpy? Basically enthalpy is insufficient as it doesn;t account for the entropy changes
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Aaradhana
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(Original post by JMaydom)
It's a measure of the energy available.... why is this harder than enthalpy? Basically enthalpy is insufficient as it doesn;t account for the entropy changes
No, I understand the concepts of both but I just don't understand the statement about the quality of energy.
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Aaradhana
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We had this simple formula. ΔStotal = ΔSsystem - (ΔHsystem/T)
Then the Gibbs guy multiplies it by (-T) and we have a new formula and that means something.

Though I understood this process, I don't get the point of it!
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username913907
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(Original post by Aaradhana)
No, I understand the concepts of both but I just don't understand the statement about the quality of energy.
well thats probs just a typo
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Borek
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Perhaps it is some obscure reference to the fact Gibbs energy is the maximum amount of non-expansion work that you can get from the system.
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Aaradhana
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(Original post by Borek)
Perhaps it is some obscure reference to the fact Gibbs energy is the maximum amount of non-expansion work that you can get from the system.
I'm sorry, what's "non-expansion work that you can get from the system", I haven't learnt about it.
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charco
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(Original post by Aaradhana)
I'm sorry, what's "non-expansion work that you can get from the system", I haven't learnt about it.
What Gibbs meant by 'free' energy is energy that is available to do work.

The energy of the universe is either dissipated and spread over all of the particles increasing their entropy, or is in the form of chemical energy (enthalpy) that can be used to do work (i.e. converted to heat energy increasing pressure of gas or converted to electrical energy etc)

So he said that as the total energy of the universe is constant (law of conservation of energy) then as the free energy decreases the universal entropy must increase as the heat is getting dissipated.

ΔG = ΔH(system) - TΔS(system)

Where

ΔG = -TΔS(universe)
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Aaradhana
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(Original post by charco)
What Gibbs meant by 'free' energy is energy that is available to do work.

The energy of the universe is either dissipated and spread over all of the particles increasing their entropy, or is in the form of chemical energy (enthalpy) that can be used to do work (i.e. converted to heat energy increasing pressure of gas or converted to electrical energy etc)

So he said that as the total energy of the universe is constant (law of conservation of energy) then as the free energy decreases the universal entropy must increase as the heat is getting dissipated.

ΔG = ΔH(system) - TΔS(system)

Where

ΔG = -TΔS(universe)
Whoa. That was really helpful! Thanks.
PRSOM
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