Explain spontaneity of a process in terms of Gibbs energy.

Explanation

Gibbs Energy : Gibbs energy is a thermodynamic function. This is the difference in the enthalpy (H) and the product of entropy (S) and absolute temperature (T) of the system.
G = H -TS
Gibbs energy is the amount of energy available from a system which can be put to useful work at constant temperature and pressure.
The change in Gibbs energy for the system `DeltaG_("system")` at constant temperature is
`DeltaG_("system") = DeltaH_("system")-TDeltaS("system")`
If `DeltaG_("system")` is negative `( lt 0) ` the process is spontaneous.
If `DeltaG_("system")` is positive `( gt 0)` the process is non-spontaneous.
If `DeltaG_("system")` is zero the system has attained equilibrium.