How does change in entropy influence the tendency of a reaction to occur?
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 $(\Delta H&lt;0)$ or weakly endothermic ($\Delta H&gt;0$ and $\Delta H &lt; T\Delta S$), 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 $\Delta G$:


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