What is entropy? Explain its role in spontaneity.

(N/A) Entropy is a measure of the degree of randomness or disorder in a system.
Entropy is lowest in the solid state and highest in the gaseous state. When heat is added to a system,it increases molecular motion,leading to increased randomness.
The change in entropy $(\Delta S)$ is defined as the heat added to the system reversibly $(q_{rev})$ divided by the absolute temperature $(T)$: $\Delta S = \frac{q_{rev}}{T}$.
For a process to be spontaneous,the total entropy change of the universe must be positive: $\Delta S_{total} = \Delta S_{sys} + \Delta S_{surr} > 0$.
$1$. If $\Delta S_{total} > 0$,the process is spontaneous.
$2$. If $\Delta S_{total} < 0$,the process is non-spontaneous.
$3$. If $\Delta S_{total} = 0$,the system is in equilibrium.
Entropy is a state function,meaning its value depends only on the initial and final states of the system.