What is the Standard State of Carbon?

[PVnRT81]

Homework Statement

Graphite can be change into diamond according to the following equation:

C_graphite ==> C_diamond

Consider the following reaction equations:

C_graphite + O_{2 (g)} ==> CO_{2 (g)} ΔH = -393.5 kJ/mol

C_diamond + O_{2 (g)} ==> CO_{2 (g)} ΔH = -393.4 kJ/mol

Which form of carbon - graphite or carbon - is considered the standard state of carbon?

2. The attempt at a solution

I tried to use Hess' Law of Summation and determined that to go from graphite to diamond, it takes -0.1 kJ/mol.

To go from diamond to graphite, it takes 0.1 kJ/mol.

I don't know how I can use this information to determine the standard state.

 

[Borek]

The one with lower energy content is the more stable one.