The standard state Gibbs free energies of formation of $\mathrm{C}$ (graphite) and $C$ (diamond) at $\mathrm{T}=298 \mathrm{~K}$ are \[ \begin{gathered} \Delta_{f} G^{o}[\mathrm{C}(\text { graphite })]=0 \mathrm{~kJ} \mathrm{~mol} \\ \Delta_{f} G^{o}[\mathrm{C}(\text { diamond })]=2.9 \mathrm{~kJ} \mathrm{~mol}^{-1} . \end{gathered} \] The standard state means that the pressure should be 1 bar, and substance should be pure at a given temperature. The conversion of graphite [ C(graphite)] to diamond [ C(diamond)] reduces its volume by $2 \times 10^{-6} \mathrm{~m}^{3} \mathrm{~mol}^{-1}$. If $\mathrm{C}$ (graphite) is converted to $\mathrm{C}$ (diamond) isothermally at $\mathrm{T}=298 \mathrm{~K}$, the pressure at which $\mathrm{C}$ (graphite) is in equilibrium with $\mathrm{C}($ diamond), is [Useful information: $1 \mathrm{~J}=1 \mathrm{~kg} \mathrm{~m}^{2} \mathrm{~s}^{-2} ; 1 \mathrm{~Pa}=1 \mathrm{~kg} \mathrm{~m}^{-1} \mathrm{~s}^{-2} ; 1$ bar $=10^{5} \mathrm{~Pa}$ ]