For 2NO2 forming N2O4, equilibrium gives [NO2] = 0.016 M and [N2O4] = 0.042 M. What is Kc?

1. The balanced equation is 2NO2 going to N2O4, so N2O4 is the single product. 2. The expression is therefore Kc = [N2O4] divided by [NO2] squared. 3. Square the reactant concentration first: 0.016 x 0.016 = 2.56 x 10^-4. 4. Divide the product concentration by that value: 0.042 / 2.56 x 10^-4 = 164. 5. Rounded to two significant figures this is Kc = 1.6 x 10^2. 6. The value 2.6 comes from dividing 0.042 by 0.016 and forgetting the square. 7. The value 0.38 inverts the ratio, putting the reactant on top by mistake. 8. Dimensional analysis would suggest a unit here, but Kc values are quoted without units. _Source: OpenStax Chemistry (CC BY 4.0), Ch 13 "Fundamental Equilibrium Concepts", section 13.2 Equilibrium Constants_