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### confused about 2nd law !!!

Posted: Wed Feb 14, 2018 10:40 am
I know that the second law of thermodynamics states that the entropy of an isolated system has a tendency to increase, but how is this law related to the equation deltaS = qrev/T ?

### Re: confused about 2nd law !!!  [ENDORSED]

Posted: Wed Feb 14, 2018 11:17 am
There are many, many formulations (statements) of the 2nd Law of Thermodynamics. They are all related to each other but sometimes in relatively difficult to derive ways that are sometimes not apparent at first glance. However, the definition ΔS = qrev/T can be used to write:

ΔStot = ΔSsys + ΔSsurr > 0 for all spontaneous processes
ΔSsys = qrev/T and ΔSsurr = -qrev/T

### Re: confused about 2nd law !!!

Posted: Fri Mar 16, 2018 4:57 pm
How do we know when to use the 2nd law or 3rd law equations? What is the main difference between these 2 laws?

### Re: confused about 2nd law !!!

Posted: Sat Mar 17, 2018 1:50 am
The third law of thermodynamics is used to analyze the probability of finding one compound in a certain direction (think Schrodinger's cat) given the different orientations that it can have. The second law of thermodynamics will involve examining what will occur to the entropy of the system/surroundings when reacted/heated/cooled