Chemistry/Biology... Thermodynamics

[mokamia00]

Hi,
I am having troubles understanding the term "stability" in chemistry, biology, biochem etc...
From what I understand, something is stable if it has a low amount of energy. Thus if it has a low amount of energy, it does not really react. But when I was reading a chapter of biochemistry about proteins, they said that when the hydrophobic portions of the proteins are inside and the hydrophilic are outside, the protein is more stable. The entropy increases. Should I consider the energy that defines stability as the entropy, enthalpy or just the Gibbs free energy? When Gibbs free energy is low (negative number) the system is more stable? Hope you understand my question, thank you

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[bee17]

We usually talk about entropy, enthalpy, and Gibbs free energy in terms of how they change during a reaction (remember, the symbol delta means change).

A positive change in entropy means that a system is becoming more disordered, while a negative change in entropy means that a system is becoming less disordered (and therefore cannot be an isolated system).
A positive change in enthalpy means that a reaction is endothermic (requires heat), while a negative change in enthalpy means that a reaction is exothermic (produces heat).
A positive change in Gibbs free energy means that a reaction is not spontaneous, while a negative change in Gibbs free energy means that a reaction is spontaneous.

The three are related by this equation:

G =

H - T

S

 

[Quinoline]

I'd say use gibbs. Like bee said,

G =

H - T

S
In the protein example, entropy decreases making G more positive, but the enthalpic H contribution outweighs this because with the hydrophic portion inside, more solvent H bonds and protein-solvent interactions are created, so overall G is more negative with the hydrophic portions inside, and this is more stable.

 

[mokamia00]

We usually talk about entropy, enthalpy, and Gibbs free energy in terms of how they change during a reaction (remember, the symbol delta means change).

A positive change in entropy means that a system is becoming more disordered, while a negative change in entropy means that a system is becoming less disordered (and therefore cannot be an isolated system).
A positive change in enthalpy means that a reaction is endothermic (requires heat), while a negative change in enthalpy means that a reaction is exothermic (produces heat).
A positive change in Gibbs free energy means that a reaction is not spontaneous, while a negative change in Gibbs free energy means that a reaction is spontaneous.

The three are related by this equation:

G =

H - T

S

Thank you

I'd say use gibbs. Like bee said,

G =

H - T

S
In the protein example, entropy decreases making G more positive, but the enthalpic H contribution outweighs this because with the hydrophic portion inside, more solvent H bonds and protein-solvent interactions are created, so overall G is more negative with the hydrophic portions inside, and this is more stable.

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