Here's a breakdown:
Spontaneous Reaction:
* Favorable: The products are more stable than the reactants.
* Energy released: The reaction releases energy (exothermic).
* Entropy increases: The products are more disordered than the reactants.
* Doesn't mean fast: The reaction might happen very slowly, even if it is spontaneous.
Non-Spontaneous Reaction:
* Unfavorable: The reactants are more stable than the products.
* Energy required: The reaction requires energy input (endothermic) to occur.
* Entropy decreases: The products are more ordered than the reactants.
* Needs external input: Won't happen on its own.
Key point:
A spontaneous reaction is not necessarily a fast reaction. Factors like activation energy, temperature, and catalysts can influence the speed of a reaction, regardless of whether it is spontaneous or not.
Example:
* Spontaneous: Rusting of iron (Fe + O₂ → Fe₂O₃) is spontaneous at room temperature, but the process is slow.
* Non-Spontaneous: The decomposition of water into hydrogen and oxygen (2H₂O → 2H₂ + O₂) is non-spontaneous under standard conditions. It requires electrical energy input to happen.
In summary:
Spontaneous reactions are those that happen naturally, releasing energy and increasing disorder. While spontaneity implies a reaction *can* happen, it doesn't tell us *how fast* it will happen.
