Pressure above which graphite will spontaneously change into diamond

[anisotropic]

Homework Statement

Calculate the pressure at which graphite spontaneously changes to diamond.

T = 298.15 K (isothermal)
V_diamond - V_graphite = -2 x 10^-6m³/mol

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

Homework Equations

Not really sure here... Could be anything.

Perhaps useful is: G = H - TS

But I don't see where P fits in.

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]

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