In Spontaneous and Non-Spontaneous Reactions process that occurs autonomously, transitioning from a nonequilibrium condition to an equilibrium state, is referred to as a spontaneous or natural process. It is unidirectional, irreversible, and a genuine process. Below are a few instances of spontaneous processes.
(i)Water flows from a higher elevation to a lower elevation. The decline cannot be rectified without external assistance.
(ii) The neutralization of a strong acid by a strong base constitutes a spontaneous acid-base reaction.
NaOH (aq) + HCl (aq) → NaCl (aq) + H2O(l)
(iii) The addition of zinc to the copper sulphate solution results in the disappearance of the blue color due to a spontaneous redox reaction.
CuSO4(aq) + Zn (s) → ZnSO4(aq) + Cu (s)
A reaction is termed a spontaneous process if it requires an initial input of energy but then progresses autonomously. The combustion of coal and hydrocarbons in the atmosphere exemplifies such spontaneous reactions. A piece of coal does not ignite in air independently; rather, the reaction is triggered by a spark, and once the coal begins to burn, the reaction proceeds spontaneously to completion.
A non-spontaneous process is the inverse of a spontaneous process. It does not transpire autonomously and is not found in nature. Reversible processes represent a boundary condition between spontaneous and non-spontaneous processes. Certain non-spontaneous processes can occur by providing energy to the system from an external source. Below are instances of nonspontaneous processes.
(i)Pumping water to a high position.
(ii) Transfer of heat from the chilly inside of the refrigerator to the warm surroundings.
(iii) The reaction of nitrogen with oxygen produces nitric oxide. This process occurs by the absorption of heat. N₂ and O₂ are present in air; however, they do not undergo chemical reactions under ordinary conditions. The reaction occurs when energy is supplied by lightning.
N2(g) + O2(g) →2NO (g) (non-spontaneous reaction)
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