Question

in thermodynamics , we only can know that weather a process will occur on not , but we are un-able to that how much time will the process take ?, why ?

Answer 1

the activation energy isn't that dependant on the spontaneity of a reaction. The kinetics of a reaction, that is, the speed at which it occurs, is highly dependant on this activation energy. For example, diamond will become graphite (pencil lead), but it only happens over millions of years because the energy needed to start the process is too high. Alternatively, some reactions, after you add the activation energy, are rapid like explosions (though it could also be slower and release the same amount of energy in the body where the process is controlled to help us move)

Yes, kinetics and thermodynamics are related but they are not the same. Thermodynamics predicts if a reaction will happen after activation energy is added, but kinetics is what determines the rate of a reaction.