Equilibrium Constant Unit Conversion

The equilibrium constant, $K_c$, for the reaction $2\mathrm{NO}_2(g) \rightleftharpoons \mathrm{N}_2\mathrm{O}_4(g)$ is 170 at 25°C. This value is based on concentrations expressed in mol/L. What is the value of the equilibrium constant for this reaction if concentrations are expressed in g/L?