How does change in entropy influence the tendency of a reaction to occur? [duplicate]








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[Spontaneity of Reactions- Gibbs Energy or Entropy change](/questions/69478/spontaneity-of-reactions-gibbs-energy-or-entropy-change)

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I know that entropy is the measure of the randomness of particles within a system, but how would it affect the tendency of the reaction? Would it just increase or decrease the chance of the reaction occurring, based on what change in enthalpy is?




**Entropy** ($S$) is a measure of the disorder in a system.


In a closed system, entropy always increases over time. In an open system, energy can be added to a system to cause a decrease in entropy, but this is not necessarily a spontaneous reaction.


A reaction will be spontaneous if the change in **free energy**, $\Delta G$, is negative.


Quantitatively, 
if entropy increases, and the reaction enthalpy is exothermic $(\Delta H<0)$ or weakly endothermic ($\Delta H>0$ and $\Delta H < T\Delta S$), the reaction becomes spontaneous according to the free energy equation. 


Since the observable universe is essentially a closed system, entropy will continue to increase until the universe essentially ceases to exist.


This way an increase or decrease(sometimes) in the randomness can cause a reaction to occur.


Here is a table relating to spontaneity and signs of $\Delta G$:
[![enter image description here](https://i.stack.imgur.com/IkkXJ.jpg)](https://i.stack.imgur.com/IkkXJ.jpg)


[Image Source](http://www.eoht.info/page/Spontaneity+table)


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