5. (12 pts) Consider the oxidation of solid nickel to form nickel oxide according to the reaction 2 N i(s)+O_{2}(g)=2 N i O(s) Knowing that metallic nickel is diluted with

inert platinum such that the activity of nickel is 0.25,calculate the lowest oxygen partial pressure (in kPa) at which nickel oxide will form. The kJ standard Gibbs energy of formation of \Delta G_{f}^{\circ}\left(\frac{k I}{m o l}\right)=-471,200+172 T