Understanding Entropy and Free Energy in Chemical Reactions

In summary: And just how is that calculated? Say I've got 10 grams of hydrogen at STP... What Gibbs free energy is appropriate for that substance?\left(\frac{1}{2.016} \frac{\mathrm{mol}}{\mathrm{g}}\right)\left[0\,\frac{\mathrm{J}}{\mathrm{mol}}-\left(298\,\mathrm{K}\right)\left(131\,\frac{\mathrm{J}}{\mathrm{mol}\cdot\mathrm{K}}\right)\right]\approx -190\,\mathrm{kJ}
  • #1
MonsieurWise
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I'm having trouble understanding why in a reaction, when the free energy G of the product equal the free energy G of the reactant, the reaction is at equilibrium. Here, as my book say, the system has reached its minimum free energy. I don't really get why... Could someone explain to me...? Thanks!
 
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  • #2
Oh...never mind. It seems like the reaction just like the Delta G, not G, to be negative to be spontaneous, right? Now The only thing I don't get is:
Since:
Gtotal = Greactant + Gproduct
when Greactant decrease, Gproduct increase, so how can it say at equilibrium, "the system has reached minimum free energy"?
Thanks
 
  • #3
MonsieurWise said:
... Now The only thing I don't get is:
Since:
Gtotal = Greactant + Gproduct
when Greactant decrease, Gproduct increase, so how can it say at equilibrium, "the system has reached minimum free energy"?
Thanks

Is it correct to say "Gtotal = Greactant + Gproduct"?

Gibbs Free Energy is the maximum amount of useful work you can obtain from a process not an inherent energy present in either the products or reactants. Where have you seen this equation? It's news to me.
 
  • #4
Oh, it was in my chemistry book...
 
  • #5
chemisttree said:
Gibbs Free Energy is the maximum amount of useful work you can obtain from a process not an inherent energy present in either the products or reactants. Where have you seen this equation? It's news to me.

The Gibbs free energy G is just the enthalpy minus TS. It's definitely an inherent property (a state function) of a substance.

MonsieurWise, the question is by what magnitude the Gibbs free energies of the reactants and the products increase and decrease. The magnitudes aren't constant; they depend on the amounts that already exist. At equilibrium, [itex]\Delta G_\mathrm{reactant}[/itex] and [itex]\Delta G_\mathrm{product}[/itex] are equal and opposite.
 
  • #6
Mapes said:
The Gibbs free energy G is just the enthalpy minus TS. It's definitely an inherent property (a state function) of a substance.

And just how is that calculated? Say I've got 10 grams of hydrogen at STP... What Gibbs free energy is appropriate for that substance?
 
  • #7
[tex](10\,\mathrm{g})\left(\frac{1}{2.016} \frac{\mathrm{mol}}{\mathrm{g}}\right)\left[0\,\frac{\mathrm{J}}{\mathrm{mol}}-\left(298\,\mathrm{K}\right)\left(131\,\frac{\mathrm{J}}{\mathrm{mol}\cdot\mathrm{K}}\right)\right]\approx -190\,\mathrm{kJ}[/tex]
 

What is entropy?

Entropy is a measure of the disorder or randomness in a system. It is often referred to as the amount of energy that is unavailable for work in a system.

How does entropy relate to the second law of thermodynamics?

The second law of thermodynamics states that the total entropy of a closed system always increases over time. This means that the disorder or randomness in a system will tend to increase, and energy will become less available for work.

What is free energy?

Free energy is a measure of the energy in a system that is available to do work. It takes into account both the internal energy of a system and the entropy of the system.

How does free energy relate to the spontaneity of a reaction?

The change in free energy, or delta G, can be used to predict the spontaneity of a reaction. A negative delta G indicates a spontaneous reaction, while a positive delta G indicates a non-spontaneous reaction.

What factors affect the entropy and free energy of a system?

Factors such as temperature, pressure, and the number of particles in a system can affect the entropy and free energy. Changes in these factors can lead to changes in the disorder and availability of energy in a system.

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