[danago]

Hi.
As part of a question i was doing, i needed to provide examples of a reaction that is:

-Spontaneous but kinetically stable
-Non-spontaneous but very fast

For the first one i just gave the example of hydrogen and oxygen reacting to form water under standard conditions.

For the second, im wondering, is there any sense in talking about a reaction that is nonspontaneous yet fast? How can a reaction be fast if it will not occur without intervention? Does it make sense to talk about a reaction that would be fast IF it did occur?

Thanks for clearing this up,
Daniel.

[BluRay]

Trick: consider the reverse reaction.

[danago]

So you're saying to consider a reaction such as 2Na⁺+H₂ 2Na+2H⁺ which is clearly not spontaneous in the forward direction but very spontaneous in the reverse direction, and also very fast in the reverse direction?

[Astrokel]

No, BluRay meant the example you stated earlier. Some non-spontaneous reaction react slowly even at high temperature.

[BluRay]

So you're saying to consider a reaction such as 2Na⁺+H₂ 2Na+2H⁺ which is clearly not spontaneous in the forward direction but very spontaneous in the reverse direction, and also very fast in the reverse direction?

Sort of.
It's better if you consider a reaction near the equilibrium: exactly at equilibrium, direct and reverse reaction have the same speed; a little off-equilibrium, if the direct reaction (spontaneous) is fast, the reverse reaction (non spontaneous) is almost as fast.