Are all spontaneous reactions irreversible?

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Vadiraj K T

Yes but only with the expenditure of energy, which is not spontaneous. as in II law of TD the entropy denotes the degree of disorderness. where as the spontaneous reaction are always leads to disorderness.

Shufeng Zhang

Entropy: A concept that is not a physical quantity

https://www.researchgate.net/publication/230554936_Entropy_A_concept_that_is_not_a_physical_quantity