Will Diamond spontaneously decompose into Graphite?

Question

I have a question in the Free Energy section of our textbook that is giving me problems. Here goes "When carbon and oxygen combine to form carbon dioxide, the reaction releases more free energy when diamond is used as a source of carbon than when graphite is used as the carbon source. Based on this information, will diamond spontaneously decompose into graphite? If it does why do we not see our diamond jewelry become pencil points? If it does not, then does this imply that diamonds will last forever?

thanks

Answer 1

Based on this information, no, a diamond will not spontaneously decompose into graphite. It also does not imply that diamonds will last forever. It only states that diamonds are a better carbon based energy source than graphite.

Answer 2

Diamond has in a lattice structure that is at a local minimum, in terms energy. To convert to graphite, you must overcome the energy of activation to convert to the more stable, lower energy of the graphite lattice structure. In an inert atmosphere, this is done slowly at 1000 deg C, or more rapidly at 1700 deg C.

Unless the ambient temperature is pretty high (1000 deg C or higher), it's is pretty thermostable.

Answer 3

This question was posed in three classes this semester (Physical Chemistry, Water Chemistry, and Advanced Inorganic Chemistry). The answer is the same. Even thought the reaction is spontaneous, the activation energy barrier is so high that the decomposion of C(dia) to C(gr) is slow enough to not be noticible even after thousands of years.


Ken

Answer 4

> will diamond spontaneously decompose into graphite?
Nope. Diamond is stable. You'd need to add energy to break the existing bonds, and then you probably wouldn't get graphite anyway.

> does this imply that diamonds will last forever?
Left to themselves, diamonds will last forever. But they're not left to themselves. They can be burned, to make carbon dioxide. They can be abraded or hammered, to make diamond dust.

Answer 5

Think "endothermic".... Remember that diamond requires centuries of heat and pressure to form the lattice.