 ##  [Second Law of Thermodynamics](/second-law-thermodynamics) 

  ##  [Second Law of Thermodynamics](https://engineering.quantumdictionary.io/second-law-thermodynamics-0) 

  
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**Engineering &amp; Applied Technologies Dictionary**

 
Definition

In a thermodynamically isolated system, the total thermodynamic entropy does not decrease over time; spontaneous processes either increase total entropy or leave it unchanged when they are reversible, establishing a preferred direction for macroscopic energy dispersal and limiting complete conversion of heat into work.

 
 ##  [Second Law of Thermodynamics](https://health.quantumdictionary.io/second-law-thermodynamics-1) 

  
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**Health &amp; Life Sciences Dictionary**

 
Definition

In a macroscopic thermodynamic context, the Second Law of Thermodynamics asserts that for an isolated system (no exchange of matter or energy) the thermodynamic entropy does not decrease over time; typical spontaneous processes increase total entropy, which determines the directionality of heat flow and the irreversibility of macroscopic transformations.