Entropy Spontaneity: Fill & Download for Free

In layman's terms? Very simply, that in any closed system entropy either stays put, or increases, and never decreases. However, the rest of the laws of physics do not stipulate this - in fact nothing in the rest of the laws of physics, as Loschmidt understood them at the time, would prohibit everything going in the reverse direction and the amount of entropy to spontaneously go back down.There are various approaches to tackling this, but the best layman's ones I know of, concern so-called Information Physics - i.e. that information is, itself, inherently tied to the arrow of time (and, by extension, entropy), and that situations where the entropy spontaneously decreases are, therefore, not observable because they leave no evidence of their happening (the principles cited by Lorenzo Maccone: notably, that Quantum mechanics is valid at all scales http://arxiv.org/abs/0802.0438).(Some argue that this line of reasoning is bogus, but I am, personally, not clever enough to discern the bogousity.)

The products of an endothermic reaction are higher in thermal energy than the reactants. It’s like a bowling ball on the side of hill has rolled uphill all on its own, instead of downhill, as it should. But thermal energy isn’t the whole story. An endothermic reaction may be spontaneous because of an increase in entropy.Spontaneity can be indicated by the sign of Gibb’s free energy, ΔG.ΔG = ΔH - TΔS where ΔH is the enthalpy change (the thermal part) and ΔS is the change in entropy.For a reaction to be spontaneous ΔG must be negative. That means that TΔS must be greater in energy than ΔH, so that when TΔS is subtracted from a positive ΔH, the result will be negative, a negative ΔG, and a spontaneous reaction.

​​​​​​​​Consider any molecule other than which are on surfaceThese molecules are under almost same strength of forces from all directions such that there are no net force on these molecules. So these molecules have maximum entropy as they are free to roam everywhere.Molecule on the surfaceThese molecules have unbalanced forces such that they have net force in downward direction. Thus they have practically least entropy and maximum potential energy. Water molecules at the surface are pulled inwards such that the surface is compressed with minimum surface area.Thus every molecule on the surface of water have its intrinsic tendency to move below to enjoy maximum entropy. (Spontaneous process) This tendency leads to the surface of water to have minimum surface area.(Definition of surface tension)Hence most of the surface tension is due to tendency of their surface molecules to gain maximum entropy.Hence most of surface tension of water is entropy driven.