Explain the spontaneity of a process.

Explanation

Spontaneous reaction :
A process is said to spontaneous if it occurs on its own intervention of any external agency of any kind.
All nautral process are spontaneous.
Entropy increases in all spontaneous process.
Change in entropy `..(triangleS)` = positive" is a condition but is not necessary and sufficient, condition for for the spontaneous nature of a reaction.
Change in enthalpy `"(triangleH)` =negative" may be a condition but not a necessary and sufficient conditionfor the spontaneous nature of a reaction.
At this jurícture, "Gibbs" introduced another thermodynamic function which involves both enthalpy. (H) and entropy (s) functions. This is known as free energy function (G). This is given by the equation, G =H-TS. G. is now referred as "Gibbs energy (or) Gibbs function.
`triangleG_(sys)` is negative" for spontaneous reactions (or) processes. Thus the spontaneity of a reaction and the algebraic signs of `triangleH, triangleS, triangleG` and the magnitude of T. can be related as follows: