Explain entropy and spontaneity.

(N/A) Entropy $(S)$ is a measure of the degree of randomness or disorder in a system. For a spontaneous process,the total entropy of the system and surroundings must increase,i.e.,$\Delta S_{total} = \Delta S_{sys} + \Delta S_{surr} > 0$.
Spontaneity refers to the tendency of a process to occur without continuous external influence. While exothermic reactions (where $\Delta H < 0$) are often spontaneous,enthalpy change alone is not sufficient to predict spontaneity. The second law of thermodynamics states that for a spontaneous process,the entropy of the universe increases.
The Gibbs free energy change $(\Delta G = \Delta H - T\Delta S)$ is the definitive criterion for spontaneity at constant temperature and pressure:
$1$. If $\Delta G < 0$,the process is spontaneous.
$2$. If $\Delta G > 0$,the process is non-spontaneous.
$3$. If $\Delta G = 0$,the system is at equilibrium.