positive entropy , thermodynamically feasible and thermodynamically unstable and so o

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universalcj
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1. what are the meanings of Thermodynamically feasible, Thermodynamically unstable and kinetically stable

2. Are those related to positive total entropy change?
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charco
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(Original post by universalcj)
1. what are the meanings of Thermodynamically feasible, Thermodynamically unstable and kinetically stable

2. Are those related to positive total entropy change?
The first term refers to the possibility of a reaction occurring. Reactions can only happen if they result in an increase in universal entropy.
The universal entropy change is equal to the entropy change of the system under consideration + the entropy change of the surroundings.
The entropy change of the surroundings can only increase if heat energy is released by the system to the surroundings. The entropy change of the system can only change if the number of particles increases.

Josiah Willard Gibbs derived an expression for this, which relates the universal entropy to the enthalpy change of the system and its entropy change.
ΔG = -TΔS(universe) = ΔH(system) - TΔS(system)
Where S = entropy
and H = enthalpy

So, a reaction is thermodynamically feasible if ΔG is negative, for this means that ΔS(universe) is positive and the reaction is possible.
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A compound is thermodynamically unstable with respect to its constituent elements if its formation enthalpy is positive.
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A substance is kinetically stable if the activation energy barrier to chemical change is so large as to make the reaction infinitely slow under the conditions stated.
A good example is the formation of graphite from diamond. This is thermodynamically feasible, but controlled by kinetics at room temperature and pressure.

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universalcj
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(Original post by charco)
The first term refers to the possibility of a reaction occurring. Reactions can only happen if they result in an increase in universal entropy.
The universal entropy change is equal to the entropy change of the system under consideration + the entropy change of the surroundings.
The entropy change of the surroundings can only increase if heat energy is released by the system to the surroundings. The entropy change of the system can only change if the number of particles increases.

Josiah Willard Gibbs derived an expression for this, which relates the universal entropy to the enthalpy change of the system and its entropy change.
ΔG = -TΔS(universe) = ΔH(system) - TΔS(system)
Where S = entropy
and H = enthalpy

So, a reaction is thermodynamically feasible if ΔG is negative, for this means that ΔS(universe) is positive and the reaction is possible.
---------------------------------------------------------------------------------------------------
A compound is thermodynamically unstable with respect to its constituent elements if its formation enthalpy is positive.
---------------------------------------------------------------------------------------------------
A substance is kinetically stable if the activation energy barrier to chemical change is so large as to make the reaction infinitely slow under the conditions stated.
A good example is the formation of graphite from diamond. This is thermodynamically feasible, but controlled by kinetics at room temperature and pressure.

I sincerely express my gratitude. So is it possible to say Thermodynamically feasible = thermodynamically unstable?
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universalcj
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so if there is anyhing possible regardless with the cost and the amount of energy, we can say the total entropy change is positive, thermodynamically feasible and unstable?
and kinetically stable means a reaction just have a high activatino energy which can prevent it from occurring? and is not releated to entropy change?
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charco
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(Original post by universalcj)
I sincerely express my gratitude. So is it possible to say Thermodynamically feasible = thermodynamically unstable?
no
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charco
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(Original post by universalcj)
so if there is anyhing possible regardless with the cost and the amount of energy, we can say the total entropy change is positive, thermodynamically feasible and unstable?
and kinetically stable means a reaction just have a high activatino energy which can prevent it from occurring? and is not releated to entropy change?
Thermodynamically feasible (also called spontaneous) means that according to the laws of thermodynamics the reaction is possible. The universal entropy change would be positive were the reaction to occur.

Kinetic stability does not relate to the entropy change, rather to activation energy.

Thermodynamically unstable is not a common term. I can only think that it refers to endothermic compounds, which are thermodynamically unstable with respect to their constituent elements.
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