Pressure above which graphite will spontaneously change into diamond

1. The problem statement, all variables and given/known data

Calculate the pressure at which graphite spontaneously changes to diamond.

T = 298.15 K (isothermal)
Vdiamond - Vgraphite = -2 x 10-6m3/mol

At 273.15K and 1 bar (105 Pa):
ΔGf graphite = 0
ΔGf diamond = 2.9 kJ/mol
i.e. graphite is the more stable and preferred form of carbon in the above conditions.

2. Relevant equations

Not really sure here... Could be anything.

Perhaps useful is: G = H - TS

But I don't see where P fits in.

3. The attempt at a solution

Well, I know G will be 0 at the pressure I am trying to identify (i.e. graphite and diamond will be in equilibrium, with equal tendency for the carbon to form either).
 

Mapes

Science Advisor
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G = H - TS is definitely relevant if you expand H by using its definition.
 

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