- #1
TS656577
- 62
- 0
How can you tell if a reaction is spontaneous?
Not necessarily. The entropy of the system can in fact decrease as long...a negative gibbs free energy corresponds to an increase in the entropy of the system
Andy Resnick said:A process is spontaneous if the Gibbs free energy is negative.
AbedeuS said:a negative gibbs free energy change corresponds to an increase in the entropy of the system
Is a correct statement... Q.
This is notYou must ask one simple
question: Does the entropy of the system increase?
? You could say that an increase in the entropy contributesA negative gibbs free
energy change corresponds to an increase in the entropy of the
system
Whatbecause the enthalpy releases energy to
the surroundings that then become "The system" in order to compensate for
the fact that the "universe" is a closed system in itself.
. Since when is the enthalpy a gauge of the overallThis is the energy released
to/absorbed by the reaction and is a gauge of the overall entropy change of
the system,
. What precisely is "overall energy change"? And why doThe gibbs
free energy, this is a measure of the overall energy change for the
reaction (and therefore entropy), a negative gibbs free energy corresponds
to an increase in the entropy of the system and therefore a spontaneous
reaction
pkleinod said:[...]
You failed to mention, however, that the particular criterion for
spontaneous change, a decrease in the Gibbs free energy change, only
applies to reactions which occur under the restraint of constant
temperature and pressure. You are in excellent company, for Andy_Resnick and Lightarrow also leave out this important qualifier.
[...]
for reactions restrained to occur at constant temperature and
volume, for example, it is the Helmholz free energy that one must use.
vivesdn said:But for a reaction to be spontaneous in human terms we need something more than just universe entropy increasing or Gibbs free energy (for constant T and P) decreasing. There ar e a number of termodynamically spontaneous reactions that will not happen un human time scales. As an example, you won't see a diamond burning at 20º even when this reaction should be spontaneous.
spontaneity in chemical physics is a different concept from kinetics
lightarrow said:A process is spontaneous if the Gibbs free energy variation is negative.
In order for a reaction to be considered spontaneous, it must occur without the input of external energy. This means that the products of the reaction must be lower in energy than the reactants.
Gibbs free energy is a measure of the energy available for a reaction to occur. A negative value for Gibbs free energy indicates that the reaction is spontaneous, while a positive value indicates that the reaction is non-spontaneous.
Yes, a non-spontaneous reaction can become spontaneous if the temperature and/or pressure is changed. For example, increasing the temperature can increase the energy of the reactants and make the reaction spontaneous.
The equilibrium constant is a ratio of products to reactants at equilibrium. If the equilibrium constant is greater than 1, the reaction is spontaneous in the forward direction. If the equilibrium constant is less than 1, the reaction is spontaneous in the reverse direction.
Yes, there are some reactions that may seem spontaneous based on the above criteria, but are actually non-spontaneous due to kinetic factors. These reactions may have very high activation energies, making them appear spontaneous but in reality, they occur very slowly.