Is decrease in enthalpy a criterion for spontaneity? Explain.

Explanation

Change in enthalpy `"(triangleH) ` =negative" may be a condition but not a necessary and sufficient condition for the spontaneous nature of a reaction.
Observe the following spontaneous reactions
`(1) H_(2(g))+1/2 O_(2(g)) Leftrightarrow H_(2)O " "triangleH^(0)=-"285.8 kJ/mole"`
2) `C_("graphite") † 2S_(g) to CS_(2(g)) " "triangleH^0="91.91 kl/mole"`
In reaction (1) `triangleH= -ve,` in reaction (2) `triangleH= +ve`
The decrease in enthalpy may be a condition but not a necessary and sufficient condition for spontaneity of reaction.