It is said that 2nd law predicts direction of spontaneous process. It does so by saying that direction of spontaneous process is that in which entropy of the isolated system increases or stays the same, it can't decrease. What about non - spontaneous processes? They are externally driven by energy input. For them to happen entropy of the isolated system must increase or stay the same since no process can happen which would decrease entropy of the isolated system, this would violate 2nd law. Thus 2nd law should predict the direction of non - spontaneous process as well as far as I understand. If so why is 2nd law almost always stated as to predict the direction of spontaneous procces? I think it is better to say that 2nd law predicts what processes are possible in nature regardless of their spontaenity. What are your thoughts? Is my reasoning correct and in harmony with 2nd law?
I think you are mixing up spontaneous process vs unspontaneous process with isolated system vs non-isolated system.
- If you state the 2nd law of thermodynamics for isolated systems then you are right in stating that the entropy will not decrease for any processes, spontaneous or not.
- If you state the law for non-isolated systems then you can only state that entropy will not decrease for spontaneous processes.
Because, as you rightly say, an unspontaneous process such as my action of willfully ordering a system will decrease it's entropy. But that is only because we then aren't including the body and the processes that produce the forces that let me create this local entropy decrease. If you included that - the whole picture, the isolated system - the 2nd law of thermodynamics does state that the entropy won't as a whole decrease.