Use the Expression for the Coulomb Potential Energy to Calculate $\rightarrow$

Use the expression for the Coulomb potential energy to calculate the energy for formation of 1 mole of sodium chloride ion-pairs,that is, the energy change for the following reaction:
Na⁺(g)+Cl^-(g) $\rightarrow$ Na⁺Cl^-(g)
Use r₁₂ = 283 pm.