Why does graphite sublimation break covalent bonds?

[RoboNerd]

Homework Statement

Multiple choice:[/B]
In which of the following processes are covalent bonds broken?
a) solid sodium chlroide melts
b) bronze melts
c) sucrose dissolves in water
d) solid carbon graphite sublimes
e) solid carbon dioxide sublimes

Homework Equations

none

The Attempt at a Solution

D is the correct answer according to my prep book, but I do not understand why this is true.

I think that sublimation is a physical change and like all physical changes we are overcoming intermolecular forces, not breaking intramolecular bonds. How is D thus true for graphite then?

Thanks!

 

[Borek]

There are no intermolecular forces in graphite. It is in a way a special case. Sublimation is just

C(s) → C(g)

but in solid C atoms are covalently bonded.

 

[RoboNerd]

Hmm. That is a very interesting thing to think about. Thanks so much for clarifying!