Spontaneous Process and Irreversibility

[Euphemia]

Hi,all
My problem is following this picture!
http://mykomica.org/boards/shieiuping/physics/src/1325318780058.jpg
If the system is isolated, dQ is always zero. S_b-S_a ≥0
And it satisfies the requirement of spontaneousness in isolated systems.
So ,I do wonder if irreversible process is always spontaneous!
Am I Right?
Euphemia

 

[D H]

Note: Your picture isn't coming across.

You have it backwards. Every spontaneous process is irreversible, but not every irreversible process is spontaneous.

 

[mrl rao]

A process which is irreversible is the one results in energy loss in the form of heat (dissipation) due to friction ,viscosity etc.As these are involved in processes other than natural ones- eg.,rubbing a stone againast a wall in vertically upward direction- irreversible processes need not be natural or spontaneous ones.