How do you calculate the units for Kc?

The units for Kc changes depending on the concentrations of each reactant and product in the equation. It can also be possible that there are no units for Kc because the concentrations at the top and the bottom both cancel eachother out. However, in other cases, this is how you would work it out:

The equation for Kc is [PRODUCTS]/[REACTANTS]. Hypothetically, if the equation was: A+ B --> C + 2D, the Kc equation would become: [C] [D]²  / [A] [B]. You would then replace the letters with the unit for concentration which is moldm^-3 so it becomes: [moldm^-3] [moldm^-3 ]²/ [moldm^-3] [moldm^-3]. Now you would simplify the top and bottom of the equation, also using the power rules whereby you would add the powers of the concentrations which are multiplied together like so: [moldm^-3]³ / [moldm^-3]². Finally, you would cancel the top and the bottom of the reaction by subtracting the total power of the bottom from the total power of the top: in this case, subtracting 2 from 3, this leaves 1 which means the unit is just moldm^-3.