[research]

hi
what is the differences btw these two terms? can you give me an example?

[Jorriss]

I haven't heard those terms in the context of organic chemistry but I'll still try.

Metastable is something that is thermodynamically not stable but can remain in its unstable form for prolonged periods (Diamond -> graphite I suspect?)

Unstable is just what unstable suggests.

[johnmalkinson]

Hi

It's easiest to think about the difference in tems of energy. A ball on top of a hill is unstable - it will roll down the hill to gain stability (at the bottom of the hill), losing energy in the process. It doesnt need to gain any energy before rolling down the hill. Now imagine a small dip or crater at the top of the hill. The ball would be more stable at the bottom of the hill, but it will happily sit in the crater. It is metastable. If, however, it gets enough energy to get over the edge of the crater (like an activation energy), it will then roll down the hill to get to a stable state. A metastable state is like a localised energy miniumum. If a molecule can overcome the energy barrier, it can become even more stable.

The diamond/graphite example is an excellent one. Diamond is metastable, but if it gets enough energy to overcome the activation energy, it will gain stability to become graphite, releasing energy.

John

[Jorriss]

Hi

It's easiest to think about the difference in tems of energy. A ball on top of a hill is unstable - it will roll down the hill to gain stability (at the bottom of the hill), losing energy in the process. It doesnt need to gain any energy before rolling down the hill. Now imagine a small dip or crater at the top of the hill. The ball would be more stable at the bottom of the hill, but it will happily sit in the crater. It is metastable. If, however, it gets enough energy to get over the edge of the crater (like an activation energy), it will then roll down the hill to get to a stable state. A metastable state is like a localised energy miniumum. If a molecule can overcome the energy barrier, it can become even more stable.

The diamond/graphite example is an excellent one. Diamond is metastable, but if it gets enough energy to overcome the activation energy, it will gain stability to become graphite, releasing energy.

John

Great explanation !

[research]

thanks for all the replies I get my answer