Are all exothermic reactions spontaneous?

Answer 1

Take the example of formation of water from Hydrogen, Oxygen this reaction highly exothermic but kinetically slow

The reaction to proceed first the reactants have to cross their activation energy barrier so that they form products giving the energy. Hence catalyst or temperature of the process plays a role in reaction to proceed spontaneously

The other example is burning of LPG gas requires ignition for reaction to gets started even though reaction is spontaneous.

Here is a video that explains spontaneity and signs of enthalpy and entropy:

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Answer 2

Owen Ambrose

No, not all exothermic reactions are spontaneous. Spontaneity of a reaction depends on both enthalpy (ΔH) and entropy (ΔS) changes. While exothermic reactions release heat (ΔH < 0), making them favorable in terms of enthalpy, if the increase in entropy (ΔS > 0) compensates for the negative enthalpy change, the reaction can be spontaneous. However, if the decrease in entropy outweighs the negative enthalpy change, the reaction may not be spontaneous.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.