# 2nd Law of Thermodynamics - Reformulation Regarding Spontaenity of Processes

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'm not sure what you are getting at, but a reversible process is non spontaneous and the total entropy change (system + surroundings) is zero, per the second law. A spontaneous process is irreversible to the total entropy change is greater than zero, again per second law. Apr 10, 2021 at 14:06
• Who says it only applies to spontaneous processes? Apr 10, 2021 at 14:13
• @Chet, I think it shouldn't, but it is mostly stated that way. Apr 10, 2021 at 14:45
• What I am saying is that for every process that happens regardless of its spontaenity entropy of the isolated system (universe is an isolated system) must increase. This is not true only for spontaneous process, but for non - spontaneous as well. There can be no process which would decrease entropy of isolated system. So, why is 2nd law usually formulated that it predicts direction of spontaneous process when it can also predict the direction of non - spontaneous process? Apr 10, 2021 at 15:25