What is the Second law of thermodynamics. How would you express it mathematically?
1 Answer
It simply says that the total entropy of the universe always increases in some way, somewhere, as time passes.
Or the two following equations:
#DeltaS_("univ","tot")(T,P,V,n_i,n_j, . . . , n_N) > 0# #DeltaS_("univ")(T,P,V,n_i,n_j, . . . , n_N) >= 0#
where we differentiate between total entropy of the universe and the stagnancy or increase in entropy of the universe due to a single isolated process.
#T# ,#P# ,#V# , and#n# are typical Ideal Gas Law variables.
This is because certain natural processes are irreversible, and as such, work/have worked to increase the total entropy of the universe in such a way that a corresponding reverse process doesn't undo the increase in entropy.
Note that (non-total)